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Scientific Books 
, S. Ninth Street, 
Philadelphia. 



GIFT OF 




ELECTRIC-WIRING, DIAGRAMS 
AND SWITCHBOARDS 



Electric-Wiring, Diagrams 
and Switchboards 



BY 

NEWTON HARRISON, E.E. 

Instructor of Electrical Engineering in the Newark Technical School 

A Work on the Theory and Design of Wiring Circuits ; being a Prac- 
tical Guide for Wiremen, Contractors, Engineers, Architects, and 
others interested in the application of Electricity to Illumination and 
Power. Contains Special Chapters on the Design of the Switch- 
board for Lighting and Power ; and on the Sizes of Wire necessary 
for Alternating Current Circuits of Single, Two, and Three Phase 
with various degrees of Inductance. Gives the important features 
now found in all large Power and Lighting Equipments, including 
the Converting Apparatus in connection with Single, Two, and Three 
Phase Currents. Calculations and Examples all limited to the use of 
Arithmetic in the Treatment of both Direct and Alternating Current 



CONTAINS ONE HUNDRED AND FIVE ILLUSTRATIONS SHOWING 
THE PRINCIPLES AND TECHNICS OF THE ART OF WIRING 



NEW YORK 
THE NORMAN W. HENLEY PUBLISHING COMPANY 

1906 



o?" 



1 
COPYRIGHT, 1906, BY 

THE NORMAN W. HENLEY PUBLISHING COMPANY 



SET UP, ELECTROTVPED, AND PRINTED BY 
THE TROW PRESS, NEW YORK, N. Y., U. S. A. 



PREFACE 

THE contents of this book cover the fundamental 
facts of wiring, as well as such of the practise as its 
modest proportions could be well expected to embrace. 
It is not offered to the reader as a scientific treatise 
though its statements will be found able to bear the 
light of scientific investigation but as a technical 
work, in which the author has made an effort to pre- 
sent the underlying principles of wiring in language 
suited to the comprehension of the general reader. 
Though framed in accordance with the technical re- 
quirements of the art of wiring, the subject matter has 
been presented with the idea and intention of making 
the reader independent of it as soon as possible. 
Though a mastery of the principles of rational wiring 
go hand in hand with its practise, it is frequently 
found easier to gain the practise than the theory. But 
it is also true that the best equipped in this particular 
field of work are those whose power lies within the 
head and hand, to an extent which makes them inde- 
pendent of text-books or other references. To gain 
this much-to-be-desired equipment, a knowledge of 
what is best and most useful must be obtained. What 
the author considers to be just such knowledge, is pre- 
sented here in a logical form, as far as its various 
successive steps are concerned. 

5 



6 PREFACE 

The elementary relationship of volts, amperes, and 
ohms is given first consideration; then the pivotal 
point of drop of potential is emphasized and ex- 
panded, and the first applications of this idea brought, 
as is believed, clearly to the reader's attention. Means 
of calculating drop, finding the circular mils of the 
wire, and arriving at its numbered gauge size without 
a table are given. This may be regarded as the pri- 
mary object of the book, and will be considered by 
wiremen who master this method as well worth the 
slight labor involved. The further expansion of the 
simple circuit into others of a more complex type rep- 
resents the next stage of progress. From this step 
on, the subject matter leads into a consideration of 
the principles of switchboard design, with reference to 
shunt and compound wound generators. The appa- 
ratus employed on switchboards is of great importance 
in electric lighting. Though, as is commonly sup- 
posed, the switchboard represents the means by which 
all important circuits are concentrated and controlled ; 
it is also the measuring and protective, as well as the 
distributing center of the electric light or power sys- 
tem. Wiring embraces this, as well as the moulding 
and pipe work, as will be readily understood by the 
intelligent reader. It is incompletely treated, however, 
unless the meaning of alternating current phenomena 
which relate to wiring; as well as simple arithmetical 
methods of getting the sizes of wire for such circuits, 
also receive careful attention. 

In this respect, the pages of this volume will prove 
of the utmost value to the student, wireman, or con- 



PREFACE 7 

tractor. It is not to be inferred from this, that such 
knowledge is at a high premium; but it may be in- 
ferred that such knowledge is often inaccurate, 
incoherently arranged, and frequently useless. For 
such reasons as these the latter part of the book was 
written, and it is hoped that it will fulfil the purpose 
held in view. All that the author cares to claim is 
the manner of presentation; as it is well known that 
the greater responsibility for those formulas and their 
derivations, which are the veritable foundations of the 
science of electricity, must fall upon such masters as 
Ohm and Helmholtz. 

NEWTON HARRISON. 
JANUARY, 1906. 



CONTENTS 



CHAPTER I 

PAGE 

Introduction Purpose of Wiring Ohm's Law Drop of 
Potential Meaning of a Milfoot Meaning of a Cir- 
cular Mil Calculation of Drop Calculation of the 
Sizes of Wire for a Given Drop Wiring Rules Cal- 
culation of Resistance for Branch Circuits What is 
Power and How Estimated 15 



CHAPTER II 

Carrying Capacity of Wires Effects of Heat upon Resist- 
ance Allowance for Heat A Simple Electric Light 
Circuit Wire of a 10 Lamp Circuit with Drop Analyzed 
The Wiedemann System of Lighting and Its Defects 
The Wiring Table How to Prepare a Table of Sizes 
and Circular Mils Examples of the Application of the 
Wiring Table and Formula Calculation of the Drop 
per 1,000 Feet per Ampere 40 

. CHAPTER IH 

Elements of a Wiring System Meaning of Mains, Feeders, 

Branches Proportioning the Drop in the Various Parts 

of the System The Center of Distribution Examples 

of the Effects of Drop in Parts of the Circuit Equaliz- 

9 



V- ' vl P * ' 0* 5 i CONSENTS 

PAGE 

ing the Pressure Dynamos for Incandescent Lighting 
Effects of Changes in the Field of Dynamos upon the 
Lighting A Wiring System with Four Centers of Dis- 
tribution The Life of a Lamp 63 



M CHAPTER IV 

easurement of Resistance Principle of the Wheatstone 
Bridge Balancing the Resistance of Four Lamps , 
Measuring a Lamp Hot and Cold Measuring Insulation 
Resistance The Insulation Resistance of Buildings 
Wired for Electric Lighting The Three Wire System 
Compared with the Two Wire Calculating the Three 
Wire System of Wiring Circuits of a Three Wire Sys- 
tem with Two Centers of Distribution Calculation of 
Pounds of Copper for Mains or Feeders . . . . 87 



CHAPTER V 

Types of Motors Connections of Motors Meaning and 
Reason for Back Electromotive Force Use of a Start- 
ing Box Method of Connecting Up a Shunt Wound 
Motor Horse Power of Motors and Efficiencies Effi- 
ciency of Motors and Size of Wires Advantage of High 
Pressures The Alternating Current for Lighting 
Meaning of Frequency or Cycles 112 



CHAPTER VI 

Reasons for Employing Conduit The Use of Cleats The 
Use of Moulding Iron Armored Conduit Enameled 
Iron Conduit Brass Armored Conduit Asphaltic 



CONTENTS ii 

PAGE 

Paper Tube or Plain Conduit Flexible Woven Conduit 
Flexible Metallic Conduit The Use of Bends, El- 
bows, Outlet and Junction Boxes Directions for In- 
stalling Conduit Conduit Jobs and Their Accessories 
Schedule for Wiring Systems . 124 

CHAPTER VII 

Requirements for Iron and Steel Armored Conduit Laying 
Out a Conduit System The Insulation of Conductors 
Mechanical Work Insulating Materials Concealed 
and Exposed Work Insulation Resistance Grounded 
Wires Soldering Solution A Distribution Sheet for 
Laying Out Wiring 143 

CHAPTER WE 

The Light of Incandescent Lamps The Power Consumed 
by Lamps per Candle Power Candle Power and Coal 
Effect of Low Pressure on Light Effects of Globes on 
Light Size of Room and Number of Lights Use of 
Side Lights and Chandeliers Color of Room Decora- 
tion and the Lighting 158 



CHAPTER DC 

Switchboards and Their Purpose The Parts of a Switch- 
board Connections of a Shunt Wound Generator 
The Circuit Breaker The Rheostat Connections of a 
Compound Wound Generator Fuses Connections of 
Two Shunt Wound Generators and Switchboard 
Equal Pressures for Both Dynamos The Bus Bars 



12 CONTENTS 

PAGE 

Back View of Switchboard Showing Wiring Connections 
for Two Shunt Machines Connections of Compound 
Wound Machines Showing Bus Bars and Equalizer Bar 
in Service Over Compounding The Series Winding 
and Its Purpose 168 

CHAPTER X 

Generators for Alternating and Direct Current Lighting 
Character of Lighting Done The Switchboard for Two 
Compound Wound Generators Connections to Instru- 
ments Switchboard for Control of Six Floors and Two 
Elevators Connecting Two Shunt Dynamos According 
to the Three Wire System at the Switchboard Switch- 
boards for Electrolytic Work 188 

CHAPTER XI 

Panel Switchboards Street Railway Switchboards Con- 
nections of Compound Wound Generators in a Power 
House to Switchboard and Instruments Lightning 
Arresters The Panels and Their Functions Station 
Fires through Lightning The Generating, Feeding and 
Metering Sections 198 

CHAPTER XII 

Testing The Ground Detector Testing with a Volt- 
meter Use of the Magneto for Testing Insulation 
Locating Grounded Circuits Damp Basements Use 
of Insulators Weatherproof Wire Cables Rotary 
Converters The Applications of Rotary Converters 
Efficiency of Converters 209 



CONTENTS 13 



CHAPTER XIII 

PAGE 

Important Features of Alternating Currents to Consider 
Losses in a Line Inductance Explained Inductance 
with Alternating Currents Resistance Compared with 
Inductance Effect of Resistance and Inductance on an 
Alternating Current Effect of Capacity on an Alternat- 
ing Current 223 



CHAPTER XIV 

Calculation of Reactance Value of Induction Reactance 
Value of Capacity Reactance Calculation of Impedance 
in a Circuit The Unit of Self Induction The Power 
Factor 233 

CHAPTER XV 

Circular Mils for Alternating Current Mains Value of C 
for Single Phase Currents Circular Mils Calculated 
for Single Phase Circuits Circular Mils Calculated for 
Two Phase Circuits Circular Mils Calculated for Three 
Phase Circuits Average Power Factors Weight of 
Copper The Induction Motor Synchronous Motors 
Rotaries in Power Transmission Rotaries in Elec- 
tric Light Stations Two and Three Phase Alternator 
Connections 242 



CHAPTER I 

INTRODUCTION. PURPOSE OF WIRING. OHM'S LAW. DROP 
OF POTENTIAL. MEANING OF A MILFOOT. MEANING 
OF A CIRCULAR MIL. CALCULATION OF DROP. CALCU- 
LATION OF THE SIZES OF WIRE FOR A GIVEN DROP. 
WIRING RULES. CALCULATION OF RESISTANCE FOR 
BRANCH CIRCUITS. WHAT IS POWER AND HOW ESTI- 
MATED. 

Introduction. Wiring is now one of the most 
important departments of electrical engineering. In 
the last 15 years it has developed from a compara- 
tively haphazard attempt to conduct current to the 
various lamps in a building into a systematized 
code of principles and practices based upon the rul- 
ings of the Board of Fire Underwriters, in conjunc- 
tion with the recommendations of the most promi- 
nent society of electrical experts in the United 
States. 

It has in fact assumed an importance in the 
building arts second to none. No large structure is 
erected at present without provision being made in 
the plans for electric wiring. In many cases it has 
entirely superseded gas and is the only means of 
lighting considered. 

The development of the art of wiring has meant 
the development of industries dependent upon it for 

15 



16 ELECTRIC-WIRING, DIAGRAMS 

their existence. Immense amounts of capital are 
in use for the manufacture of insulated wire of 
many descriptions ; for the manufacture of sockets, 
switches, cut-outs, lamps, lampcord, iron pipe con- 
duit, and a host of smaller appliances essential to 
the installation of a wiring system. The experi- 
mental stage has been passed and electric wiring 
and electric lighting have entered into the admin- 
istration of the affairs of our large cities as an 
economic measure required for public safety and 
convenience. So we enter, as it were, upon a new 
era in the application of electricity for electric light 
and power, and this has had enormous influence 
upon the development and progress of every large 
city and town. 

Regarding the practice of wiring from such stand- 
points, it is easy to understand the importance to 
be attached to those principles which lie at the very 
root of the subject. When it is remembered, that 
the greater part of the wiring is still to be done in 
thousands of homes and buildings of the future; 
that the universal application of electricity for elec- 
tric lighting will become a fact as soon as the price 
of electricity is within the means of the humbler 
classes, and finally that its hygienic benefits are so 
pronounced both in summer and winter that it must 
in the course of time be regarded as an indispen- 
sable adjunct to home comfort; it will be seen that 
the art which will reach its greatest development 
and application in that direction for that purpose is 
electric wiring. 



AND SWITCHBOARDS 17 

Statistics may be found in a variety of magazines 
showing the enormous growth of electric lighting 
in the United States, but one of the most unique 
records is that of the fan motor load which is ex- 
perienced at certain hours of the day in large cities 
during the summer months. 

Recently the New York Stock Exchange expended 
thousands of dollars in the construction of an equip- 
ment, largely electrical, for keeping the air of the 
exchange 10 degrees cooler than the air of the street 
during the heated period. Fans 12 feet in diameter 
are employed for this purpose attached to powerful 
motors. The air is filtered as it passes through into 
the exchange thus relieved of every particle of dust. 

Purpose of Wiring. It is not only the distribu- 
tion of current which is kept in view by laying out 
a wiring system, but the proportioning of the sizes 
of wire employed so as to limit the loss of pressure 
from point to point as required. In the lighting of 
incandescent lamps it is necessary to supply a defi- 
nite pressure to the terminals in order to produce 
the requisite light. The incandescent lamp is pecul- 
iarly sensitive to changes of pressure, losing a large 
percentage of its illuminating power with a slight 
drop in pressure and gaining rapidly in candle 
power as the pressure increases. The life of the 
lamp is seriously affected by more than the neces- 
sary pressure ; it rapidly blackens and soon becomes 
valueless unless such irregularities are checked in 
the power supply. 

Ohm's Law. Few discoveries of modern times 



i8 ELECTRIC-WIRING, DIAGRAMS 

rank in importance with the discovery of Ohm's 
Law. A study of the principles of electric wiring 
cannot be carried on without the reader possessing 
a thoroughly intelligent conception of the meaning 
and application of this law. 

The law in itself is exceedingly simple, and ex- 
presses the relationship between amperes, volts and 
ohms. In order to understand the law the first 
thing to be done is to gain a knowledge of what is 
meant by a volt, an ohm and an ampere. In order 
to do this satisfactorily, illustrations must be em- 
ployed which though not presenting an ideal simile, 
yet will serve to convey the idea in view. 

Volts. When a current of electricity passes 
through a circuit it is set into motion by what is 
termed electromotive force. If it is impossible to 
imagine water or steam or any other fluid passing 
through a pipe without pressure, it is likewise im- 
possible to imagine a current flowing through a cir- 
cuit without electromotive force. In other words, 
the force which moves or tends to move electricity 
is electromotive force. 

Electromotive force is measured in volts just 
as steam pressure comparatively is measured in 
pounds. The general expression, electromotive 
force and its measurement in volts, may be under- 
stood by reference to the general expression, press- 
ure and its measure in pounds. 

Amperes. If a certain quantity of electricity can 
be delivered by a current in one second it is because 
the current has a certain strength. If the current 



AND SWITCHBOARDS 19 

is capable of delivering twice as much in one case 
as another in one second, it obviously possesses 
twice the strength. A unit quantity of electricity 
is called a coulomb. The question now is, what 
is a coulomb? It can be answered in a practical 
manner by stating that every particle of copper, 
silver, gold, nickel or any other metal in an electro- 
plating bath is carried over and deposited on the 
articles to be plated, thickly or thinly, according 
to the number of coulombs that have been em- 
ployed. For instance, one coulomb per second will 
carry over one-twenty-ninth of an ounce of copper 
in an hour. Each coulomb always carries over a 
definite quantity. Each second the same amount 
is carried over, so that in the course of one hour 
(or 3,600 seconds) a weight of copper equal to one- 
twenty-ninth of an ounce has been deposited. 

A current of electricity which will give one cou- 
lomb per second has a strength of one ampere. 
This means that a current of one ampere will plate 
over a weight of copper equal to one-twenty-ninth 
of an ounce per hour. If the current has a strength 
of two amperes it will plate twice as much per 
hour, and so on. A current of the strength of five 
amperes will give five coulombs per second, ten 
amperes ten coulombs per second, etc., as indi- 
cated in the table: 



20 ELECTRIC-WIRING, DIAGRAMS 

TABLE SHOWING RELATION BETWEEN COULOMBS AND AMPERES. 



Strength 


of current. Amperes. 


Coulombs per second. 




I 


I 




2 


2 




3 


3 




4 


4 




5 


5 




10 


10 




50 


5 




IOO 


IOO 



TABLE SHOWING RELATIONSHIP BETWEEN COULOMBS, COJ-PER 
DEPOSITED AND STRENGTH OF CURRENT. 



Amperes. 


Coulombs. 


Hours. 


Pounds. 


Ounces. 


Grains. 


I 


36,000 


10 






180 


5 


l8o,OOO 


10 




2 


26 


10 


360,000 


10 




4 


5 2 


20 


720,000 


10 




8 


104 


30 


l,o8o,OOO 


10 




12 


i.S6 


40 


1,440,000 


10 


I 




208 


50 


1,800,000 


10 


I 


4 


260 



It is of great importance to grasp the meaning 
of Ohm's Law, not only as an abstract relation- 
ship between current, electromotive force and re- 
sistance, but as a physical relationship, which may 
be proved by illustration in many ways. The fol- 
lowing tables are illustrative of the application of 
Ohm's Law in three successive cases in which the 



AND SWITCHBOARDS 



21 



current remains constant, the volts constant and 
the resistance constant. The influence of this con- 
dition is interesting in each table and shows that 
either amperes, volts or ohms can be calculated 
by knowing the other two, as follows: 

Table I Amperes = volts -=- ohms. 
Table II Volts = amperes X ohms. 
Table III Ohms = volts -f- amperes. 



Table I. C = E -f- R. 
CURRENT REMAINS CONSTANT. 



Amperes. 


Volts. 


Ohms. 


10 


IO 


I 


10 


20 


2 


10 


30 


3 


IO 


40 


4 


IO 


50 


5 



Table II. E = C X 
VOLTS REMAIN CONSTANT. 



Amperes. 


Volts. 


Ohms. 


10 


IOO 


IO 


20 


100 


5 


30 


IOO 


3-333 


40 


IOO 


2-5 


50 


IOO 


2.O 



22 ELECTRIC-WIRING, DIAGRAMS 

Table III. R=E-4-C. 
OHMS REMAIN CONSTANT. 



Amperes. 


Volts. 


Ohms. 


10 


TOO 


IO 


20 


2OO 


10 


30 


3 00 


IO 


40 


4OO 


IO 


50 


500 


IO 



In the cases cited E is divided twice, once by R 
and once by C, and R and C are multiplied together. 
So it is easy to remember that the two factors mul- 
tiplied together are the two which are respectively 




FIG. i. Diagram of Ohm's Law. 

divided into E to get either C or R. For instance 
E -^ by either C or R = either R or C, and C X R 
= E, which might be represented by the following 
sketch : 



AND SWITCHBOARDS 53 

The two lower ones multiplied give E (Fig. i) ; 
the upper one, divided by either of the lower, gives 
the remaining character. It is very convenient to 
those unaccustomed to algebraic forms to carry an 
image in the mind as indicated above with the 
method of handling it. 

Drop of Potential. A fact with which every one 
should be familiar is that it is impossible to trans- 
mit power from place to place without a loss. If 
steam is sent through a pipe to run an engine, the 
longer the pipe the greater the loss of power be- 
fore the steam is utilized. The smaller the diame- 
ter of a pipe the greater the waste of power in trans- 
mitting. The same principle applies to wire rope 
transmission, in which a very large percentage of 
power disappears between the points sending and 
receiving it, as in the case of cable car systems, 
passenger elevators, etc. 

A wire conducting electric power is subject to 
the same law, which manifests itself in two ways; 
first, the pressure or voltage diminishes ; secondly, 
the wire develops heat. The loss of pressure, 
which may be shown by the voltmeter, can be 
readily calculated by Ohm's Law: 

Drop = amperes X ohms. 

For instance, if the problem were given : what 
is the drop of potential in a line of 10 ohms resist- 
ance carrying a current of 10 amperes? the answer 
would be 

Drop = 10 X 10 = 100 volts. 



2 4 



ELECTRIC-WIRING, DIAGRAMS 



Rule. To calculate the drop in a line multiply 
the amperes by the ohms. 

TABLE SHOWING DROP IN A LINE. 



Size of wire 
No. 10 B & S. 


Amperes. 


Ohms. 


Drop in volts. 


i ,000 feet 


IO 


I 


IO 


2,000 feet 


10 


2 


20 


3, ooo feet 


10 


3 


30 


4,000 feet 


IO 


4 


40 


5, ooo feet 


IO 


5 


50 



It is evident from an inspection of the table that 
the drop increases as the resistance or current in- 
creases. The loss of power in a line can be dimin- 
ished by reducing the current in the line or reduc- 
ing the resistance of the line. 

Resistance of Wires. The resistance of a wire 
depends upon the length of the wire, its diameter 
or cross section, and the metal of which it is com- 
posed. Resistance is a native property, such as 
elasticity, ductility, malleability, and depends upon 
the quality or purity of the metal, or the mixture 
composing the alloy, a's in the case of german silver 
wire. 

If conductors had no resistance, no power would 
be wasted in transmitting current. In addition, a 
very small voltage would be sufficient to send 
heavy currents through a wire. On account of the 
resistance of a wire being governed by its geomet- 



AND SWITCHBOARDS 



rical dimensions, certain rules have been adopted 
by means of which the resistance of copper wires 
of any length or cross section can be readily cal- 
culated. The basis which can be employed is the 
resistance of one foot of copper wire, one one- 
thousandth of an inch in diameter, commonly 
called a milfoot, which has a resistance of a little 
less than n ohms. The term mil is employed be- 
cause it means a thousandth of an inch, or a thou- 
sandth part, and refers in this case to a round 
wire of the diameter above mentioned. If two 
such wires are placed side by side the resistance 
is reduced to one-half, three such wires will reduce 
it to one-third, etc. In other words, a rule may be 
stated as follows : 

Rule. The resistance of a wire of fixed length 
is inversely proportional to its cross section. 

It is customary to call a wire of one mil diameter 
a circular mil ; a wire of two mils diameter would 
therefore have four circular mils ; a wire of three 
mils diameter, nine circular mils, etc. 

TABLE SHOWING RELATION BETWEEN RESISTANCE AND CROSS 
SECTION. 



Circular mils. 


Ohms. 


Feet. 


IO,OOO 


I.O 


1,000 


20,000 


5 


1,000 


30,000 


3333 


1,000 


40,000 


.2500 


1,000 


50,000 


.2000 


1,000 



26 



ELECTRIC-WIRING, DIAGRAMS 



It is not necessary to show how the resistance 
increases or diminishes as the wire increases or 
diminishes in length, while retaining the same cross 
section in circular mils, because it is obvious that 
a current must move through twice as much re- 
sistance in 1,000 feet of wire as 500 feet of the same 
cross section. As a proof of this fact the drop of 
potential with a given current in a fixed cross sec- 
tion is just twice as great with twice the length 
of wire, but as drop of potential equals C X R it 
is evident that if the current remains constant the 
drop in both can only increase or double if the 
resistance doubles. 

A simple and practical rule can be deduced from 
these facts which will assume the following form : 

Rule. The resistance of a wire is proportional 
to its length in feet and inversely proportional to 
its cross section in circular mils. 



TABLE SHOWING RELATION BETWEEN RESISTANCE, CROSS 
SECTION AND LENGTH. 



Circular mils. 


Ohms. 


Feet. 


10,400 


10 


10,000 


5,200 

2,6oo 


1O 
IO 


5,000 
2,500 


1,300 
. 650 


IO 
IO 


1,250 
625 



Calculating Drop in Volts. In a single circuit 
the calculation of the drop of pressure is made by 



AND SWITCHBOARDS 



27 



using Ohm's Law in the form previously given: 
E = C X R, or volts drop = amperes X ohms. For 
instance, what is the loss of volts in a simple cir- 
cuit whose resistance is 10 ohms carrying a cur- 
rent of 3 amperes? According to the rule drop in 
volts = 10 ohms X 3 amperes or 30 volts. If the 
circuit is supplying current to lamps, then the volts 
are no where the current enters; where it leaves 
in the above case, it would be 30 volts less,. or only 
80 volts (Fig. 4) ; 30 volts disappearing through 
the effect of the resistance and current. 



+o 



LAMP 

B OHMS I O 

4 VOLTS DROP 



LAMP 1 



O 



VOLTMETER VOLTMETER 

FIG. 2. Lamps in Series, 4 Volts per Lamp. 

In the sketch (Fig. 2) the lamps are shown in 
series with each other; that is, the same current 
passing through one lamp after the other. As two 
amperes pass through each lamp as indicated, and 
as each lamp has two ohms resistance, the drop 
between the ends of each lamp would be 2 X 2 = 4 
volts. Voltmeters are shown in position across the 
terminals, each giving a reading of four volts, which 



28 ELECTRIC-WIRING, DIAGRAMS 

is a reading of the drop taking place in the lamp. 
An experiment of this kind can be tried with five 
no volt lamps arranged as shown. Only one volt- 
meter is necessary for readings from every lamp. 
When they have all been obtained their sum will 
equal the total voltage applied. 

Series Electric Lighting. A very practical ex- 
ample of the above case of series lighting can be 
found in high tension arc lighting (Fig. 3), so uni- 



DYN. 
O 1 500 V. 



50 V. 50 V 50 V. 50 V. 50 V. 



50 V. 50 V. 50 V. ' 50 V. 50 V. 



FIG. 3. High Tension Arc Light System, Series Wiring. 

versally employed in large cities. The lamps are 
placed on street corners as a rule, and extend 
through the city in this manner for a distance of 
several miles. A current of about 10 amperes is 
employed, and each lamp has the equivalent of a 
resistance of 5 ohms. According to these figures 
each lamp will have a drop of 50 volts ; therefore, 
if 10 lamps are lit, 500 volts are required, for 20 
lamps 1,000 volts, 40 lamps, 2,000 volts, etc. In a 
lighting system of this kind all wiring is done in 
series, in contradistinction to incandescent light 
wiring, which is done in multiple. The difference 
between the series system and the multiple system 



AND SWITCHBOARDS 29 

of wiring is readily illustrated by a simple sketch 
(Fig. 4)- 



-hO 




FIG. 4. Incandescent Light System, Multiple Wiring. 

Multiple Wiring. In a multiple circuit the cur- 
rent divides up ; each part of the circuit taking 
current according to its resistance, as shown by 
Ohm's Law. In the cases mentioned three amperes 
divide up into three separate currents of one am- 
pere apiece. The current divides as shown because 
the resistance of each branch will not permit any 
more to pass through. 

Example: The lamps each take i ampere at no 
volts, what is the resistance of each lamp? Refer- 
ring to the table previously given, it will be seen 
that this is a case where volts and amperes are 
given to find ohms. According to the rule, volts 
divided by amperes gives ohms; therefore no 
divided by i gives no ohms per lamp. 

What is Meant by Percentage of Drop. The 
drop in either a series circuit or a multiple circuit 
is calculated from the amperes and ohms of the cir- 
cuit. A very simple formula is employed for the 
purpose of obtaining the size of wire in circular 
mils, in which a stated loss of volts occurs. For in- 
stance, if a building is wired for incandescent lights, 



3 o ELECTRIC-WIRING, DIAGRAMS 

it is customary to make an allowance beforehand 
for the drop in volts. This allowance may be 2 
per cent., 3 per cent., etc., as the circumstances 
warrant. If no volts are supplied to the lamps, 
2 per cent, or 2.2 volts will be purposely wasted 
in the circuits before it reaches the lamps. The 
lamps will therefore receive only 107.8 volts. In 
using the formula the number of volts to be dissi- 
pated in the circuit under consideration must be 
given. 

Formula : Circular mils = feet of wire X amperes 
in wire X n -T- volts drop in wire. 

Example : Take a circuit 250 feet long carrying 
IO amperes, in which 3 volts drop will be allowed, 
how many circular mils cross section must be sup- 
plied for the wire? According to the above, a cir- 
cuit with a 250 foot run must have 500 feet of wire, 
giving circular mils equal to 500 XioXn-H3 = 
18,333. The formula is given in symbols in the 
following form : 

r iwr I* XF X A 
C. M.= -y--' 

where F = feet of wire, A = amperes, u is a con- 
stant, V volts drop and C. M. = circular mils. 
The constant n is the resistance in ohms of i mil 
foot of copper wire. 



AND SWITCHBOARDS 



3 1 



TABLE SHOWING EFFECT OF PERCENTAGE OF DROP ON CIRCULAR 
MILS OF WIRE REQUIRED. 



ii x F x A 
Formula: = C. M. 



^Pe-. *%%* 


Circular 
mils. 


Feet of 
wire. 


Volts drop. 


IO 


I 


IOO,OOO 


1,000 


I.I 


10 


2 


50,000 


1,000 


2.2 


IO 


3 


33*333 


I,OOO 


3-3 


10 


4 


25,000 


1,000 


4-5 


IO 


5 


20,000 


1,000 


5-5 



Volts for lighting = no. 

The volts supplied are supposed to be fairly con- 
stant ; the amperes may vary according to the num- 
ber of lamps burning. The amount of copper is 
well represented by the circular mils in each case 
where the percentage of drop is varied. With 5 
per cent, drop only one-fifth of the copper required 
in the first case is necessary. 

Sizes of Wire and Circular Mils. The sizes of 
wire are known by reference to the number of cir- 
cular mils they represent and vice versa. The num- 
ber of circular mils of a round wire may be ob- 
tained by squaring the diameter of the wire in mils. 

For instance, a wire one-tenth of an inch in 
diameter is -$, or 100 mils in diameter; the 
square of 100 mils is 100X100=10,000 circular 
mils. 



32 ELECTRIC-WIRING, DIAGRAMS 

Resistance and Circular Mils. For practical pur- 
poses it is safe to assume n ohms resistance for 
a wire I foot in length and one circular mil in cross 
section. Therefore the resistance of a wire i foot 
long and having two circular mils cross section will 
be one-half of n ohms or 5.5 ohms. On this basis 
fewer circular mils to a wire mean more resistance 
and more circular mils mean less resistance. The 
resistance of wires can be calculated by a simple 
formula which expresses the idea just stated in a 
concise form. 

Formula : Resistance in ohms equals feet of wire 
X ii -f- circular mils. 

Example: For instance, what is the resistance 
of 100 feet of wire of 1,000 circular mils? The 
answer is, ohms equals 100 X n -r- 1,000= i.i 
ohms. 

From the foregoing it is not a difficult task to 
arrange a table showing the relationship existing 
between the length of a wire, its cross section in 
circular mils and its resistance in ohms. 



AND SWITCHBOARDS 



33 



TABLE BASED UPON THE FORMULA, SHOWING THE RELATION 
BETWEEN OHMS, FEET OF WIRE AND CIRCULAR MILS. 



Formula: R = 



i r X ft. wire 
Circular mils. 



Circular mils. 


Ohms. 


Feet wire. 


1,000 


II.O 


I,OOO 


2,OOO 
3,000 


5-5 
3.666 


1,000 
1,000 


4,000 


2-75 


1,000 


5,000 


2.2 


1,000 


10,000 


I.I 


1,000 



With the number of feet of wire constant, the 
resistance is inversely proportional to the circular 
mils. For instance, with C. M. = i,ooo, R=n 
ohms, but with C. M.= 10,000, R=I.I ohms, 
showing that with 10 times the cross section the 
resistance becomes one-tenth. 

Resistance in Multiple. Calculating the joint re- 
sistance of a number of resistances in multiple can 
be accomplished at once if the resistances in mul- 
tiple are equal in the first case, or by a simple cal- 
culation if the resistances in multiple are unequal 
in the second case. 

Resistances are Equal. When resistances are in 
multiple and are equal to each other take the resist- 
ance of one and divide it by the number of resist- 
ances. 

Example: For instance, take a circuit consisting 



34 ELECTRIC-WIRING, DIAGRAMS 

of 20 lamps in multiple each having a resistance of 
100 ohms, what is the total resistance? The total 
resistance is equal to the resistance of one lamp, 
which is 100 ohms, divided by the number of lamps, 
which is 100 -=- 20 = 5 ohms. 



EQUAL RESISTANCES IN MULTIPLE. 



Formula: R = of^branch 

number of branches. 



Number of resistances. 


Resistance of each. 


Total resistance. 


50 


i ,000 ohms 


20 ohms 


40 


800 ohms 


20 ohms 


3 


600 ohms 


20 ohms 


2O 


400 ohms 


20 ohms 


IO 


200 ohms 


20 ohms 


5 


100 ohms 


20 ohms 



In dealing with incandescent lamps a fact to be 
remembered is that the resistance of the lamp cold 
is much greater than its resistance hot. A 16 cp., 
no volt lamp cold, has a resistance of 450 ohms ; 
when it is burning its resistance drops to about 120 
ohms. Therefore if a bank of lamps is measured 
cold, when in multiple, the resistance will be much 
higher than when its total resistance is calculated 
from the volts and amperes required when lighted. 

Resistances are Unequal. When resistances in 
multiple are unequal a simple calculation is em- 
ployed. The rule is as follows : The total resistance 



AND SWITCHBOARDS 35 

is equal to the reciprocal of the sum of the recipro- 
cals of the resistances. The practical application 
of the rule can be best shown by a case in point. 
Example : What is the resistance of the following 
resistances in multiple: 5, 10, 15 and 20 ohms? 
According to the rule 



In other words, add the fractions together whose 
numerators are now one, and whose denominators 
are the various resistances in multiple. In the 
above case R = i -:- = f = 2.4 ohms. It will 
be noted that the resistance of a group of unequal 
resistances in multiple is always less than the low- 
est resistance of the group. For instance, in the 
case just given the total resistance 2.4 ohms is less 
than the lowest resistance of the group, which is 
5 ohms. Adding up the reciprocals of the resist- 
ances and inverting the fraction explains the above 
process. To illustrate, take the resistances i, 2, 3, 
4 and 5 ohms in multiple, what is their total resist- 
ance? If the reciprocals are added together the 
fraction obtained is ^-. Inverting this fraction 
gives the answer T 6 ^j- = .438 ohm. If the various 
resistances in multiple are fractional they must be 
treated in the same manner, although the reciprocal 
of fractions such as ^ is 2, J is 4, etc. 



ELECTRIC-WIRING, DIAGRAMS 



UNEQUAL RESISTANCES IN MULTIPLE. 



Formula 



: R - ,+ ( R rf J 



R rf 



+ etc 



. ) 



Resistance in 

multiple. 

Ohms. 



Sum of reciprocals of resistances. 



Total 

resistance. 

Ohms. 



1,2,3 

1,2,3,4 

1.2,3,4,5 



+ i + * + i-.., H 



10, 20, 30, 40, 50, 60 
2, i, 3, F 
"1 0", 2tF> TO, 4~0, 3~0 



2+4+3+8 17 

10 + 20+30+40+50 150 



545 
.480 

4.081 
!oo666 



Examples of Drop of Potential. The drop of 
pressure in a circuit is not the only instance of a 
waste of energy met with in actual practice. The 
dynamo is also affected in its most vital part by 
the passage of a current through conductors, which 
while performing the function of generating elec- 
tromotive force, are at the same time acting in the 
capacity of conductors which possess resistance 
and develop drop in the operating machine. The 
part referred to is the armature, and allowance 
must be made for this deficiency when the dynamo 
is running at one-quarter, one-half, or full load. 
Take the case of a loo-light generator ; its amperes 
at no volts pressure are approximately 50, if the 
armature resistance is one-tenth of an ohm, the 
drop at the indicated points of load will be re- 
spectively : 



AND SWITCHBOARDS 37 

Drop at one-quarter load = 12. 5 amperes X -I 
ohm = 1.25 volts. 

Drop at one-half load = 25.0 amperes X -i ohm 
2.50 volts. 

Drop at full load = 50.0 amperes X -i = 5oo 
volts. 

It is but natural to suppose that this will have 
its effect upon the candle power of the lamps. 
At full load a no volt lamp will receive only 105 
volts, which will mean a great depreciation in illu- 
minating power, sufficient perhaps to make electric 
lighting on this basis an expensive luxury. 

A modern dynamo is built to automatically build 
up its electromotive force as the load increases. 
Such dynamos are called compound wound dyna- 
mos, and are of immense service in comparison 
with the older type, in which regulation was only 
obtained by hand. 

In an electric light system the following items 
must be considered: 

Drop in the armature. 

switchboard, 
mains, 
feeders, 
branches. 

The drop in the armature need not be considered 
as part of the drop in a wiring system, although 
indirectly it contributes to the difficulty of solving 
special problems. Loose joints and poor connec- 
tions were a source of great danger and loss of 
power, in wiring of the past decade, but the severe 



38 ELECTRIC-WIRING, DIAGRAMS 

inspection of to-day has obliterated such evils. It 
is within the province of a treatise on wiring to em- 
brace all questions relating to the passage of the 
current after leaving the dynamo. As the ultimate 
object of wiring is to limit the waste of power and 
the amount of copper employed, as well as to se- 
cure good candle power for the lamps, data on all 
three is of the utmost importance in the considera- 
tion of wiring for power and distribution of power. 
Calculation of Power. Power is calculated in 
watts. Watts are equal to the product of volts by 
amperes. If either the volts or amperes of a cir- 
cuit are increased or diminished, the power will be 
correspondingly increased or diminished. For in- 
stance, what is the power obtained from no volts 
and 25 amperes? The answer is 25 X 110 = 2,750 
watts. The watts can be still further transformed 
in horse-power by dividing them by 746. There are 
746 watts in a horse-power, therefore 2,750 watts 
-r- 746 = 3.68 horse-power, generally denoted by the 
symbols hp. 



POWER TABLE, SHOWING RELATIONSHIP BETWEEN WATTS, VOLTS 
AND AMPERES. 



Volts. 


Amperes. 


Watts. 


Horse-power. 


Kilowatts 


1,000 


IOO 


100,000 


134.0 


IOO 


500 


2OO 


100,000 


134.0 


IOO 


250 


400 


100,000 


134.0 


IOO 


I2 5 


800 


100,000 


134.0 


IOO 



AND SWITCHBOARDS 39 

Kilowatt. The kilowatt simply means 1,000 
watts, and roughly represents i hp. Manufactur- 
ers rate their dynamos on this basis instead of 
speaking of their horse-power or lighting capacity 
in lamps. The power consumed by an incandescent 
lamp varies from 3 to 4 watts per candle power. 
A 16 cp. lamp takes from 48 to 64 watts. A horse- 
power would supply power for from n to 15 lamps, 
depending upon their rating per candle power. 



40 ELECTRIC-WIRING, DIAGRAMS 



CHAPTER II 

CARRYING CAPACITY OF WIRES. EFFECTS OF HEAT UPON 
RESISTANCE. ALLOWANCE FOR HEAT. A SIMPLE ELEC- 
TRIC LIGHT CIRCUIT. WIRE OF A IO LAMP CIRCUIT 
WITH DROP ANALYZED. THE WIEDEMANN SYSTEM OF 
LIGHTING AND ITS DEFECTS. THE WIRING TABLE. 
HOW TO PREPARE A TABLE OF SIZES AND CIRCULAR 
MILS. EXAMPLES OF THE APPLICATION OF THE WIRING 
TABLE AND FORMULA. CALCULATION OF THE DROP 
PER 1,000 FEET PER AMPERE. 

Carrying Capacity of Wires. If the drop of po- 
tential in electric light wires was the only thing to 
be feared, it would be a matter of concern only to 
the consumer of electricity and the power company. 
The candle power would not be up to the standard, 
and the waste of power in the conducting wires 
would represent a heavy percentage of the cost of 
transmission. But this is not all, and the matter 
is of importance to the community as well, because 
when excessive energy is wasted in the conducting 
wires, not only does it become manifest as drop of 
pressure but as heat. The danger of an unusual 
rise of temperature in the wires is removed by the 
limitations imposed on contractors in the United 
States. These may be found in the National Elec- 
trical Code of the Fire Underwriters. 



AND SWITCHBOARDS 41 

Rubber Covered Wires. The wire employed in 
electric wiring is protected by a rubber covering, 
the name generally applied being " rubber covered 
wires." A rise in temperature of 30 degrees F. is 
allowed in such wires, and as this means an in- 
crease in resistance and therefore an increase in 
drop, the following table is given for the purpose 
of illustrating this fact: 



EFFECT OF TEMPERATURE UPON RESISTANCE OF WIRES AND DROP 
OF PRESSURE. 

1,000 feet No. 10 B. & S. = i ohm. 



Current. 


Increase in 
temperature. 


Increase in 
resistance. 


Increase 
in drop. 


10 


10 degs. F. 


.022 ohm 


.22 volts 


IO 


20 degs. F. 


.044 ohm 


.44 volts 


IO 


30 degs. F. 


.066 ohm 


.66 volts 


IO 


40 degs. F. 


.088 ohm 


.88 volts 


IO 


50 degs. F. 


.noohm 


i.io volts 


10 


75 degs. F. 


.165 ohm 


1.65 volts 


10 


100 degs. F. 


.2 20 ohm 


2. 2O VOltS 



This table is based upon the increase in resist- 
ance in a copper wire due to an increase in tem- 
perature. A rise of I degree F. means an increase 
in resistance of .0022 per cent, (nearly J of I per 
cent.). The formula employed is as fellow's : 

Formula : Resistance at an increased temperature 
= resistance of wire in ohms X .0022 X rise in de- 
grees Fahrenheit -j- the resistance of the wire. 



ELECTRIC-WIRING, DIAGRAMS 



To illustrate, supposing a wire has 5 ohms re- 
sistance and the rise in temperature is 20 degrees 
F., what is the resistance? The resistance = 5 
X .0022 X 20 + 5 = 5.22 ohms. The resistance of 
wires of other metals than copper can be calculated 
by the same formula provided the constant is ob- 
tained from the table of constants given under the 
heading of " Temperature Coefficients." 

TEMPERATURE COEFFICIENTS. 
PERCENTAGE INCREASE OF RESISTANCE PER i DEGREE FAHRENHEIT. 



Percentage. 


Metal. 


30 degrees F. 


.0021 c6 


Copper. . 


.06468 


.002^17 


Iron 


O7CCT 


.000244 


German-silver 


w / DD A 

OO732 


.001^72 


Platinum 


~ KJ I o^ 

.041 1 6 


.002167 


Aluminum 


.06501 









Calculation of a Simple Circuit. Because the 
lengths of wire connected to each lamp are differ- 
ent, the resistance of each circuit and therefore the 
drop of pressure is different. In the circuit illus- 
trated, the drop of each lamp becomes greater the 
further it is removed from the source of the supply 
of power : 

For instance (Fig. 5), lamp No. i has 100 + 100 
= 200 feet of wire connected to it, and lamp No. 
10 has 200+180+180 = 560 feet of wire in its 
circuit. The other lamps have lengths of wire in 
their circuits lying between 200 feet and 560 feet. 



AND SWITCHBOARDS 



43 



For this reason it is evident that the resistance in 
circuit with each lamp is different and therefore the 




FIG. 5. Analysis of a 10 Lamp Circuit. 

drop is unequal throughout the line. Using No. 10 
wire and allowing one ampere per lamp gives the 
following data : 

CIRCUIT OF 10 LAMPS TAKING i AMPERE APIECE. SIZE WIRE, 
No. 10 B. & S. 



Position of lamp. 


Feet of wire. 


Resistance. Ohm. 


No. i 


2OO 


.2OO 


No. 2 


240 


.240 


No. 3 


280 


.280 


No. 4 


320 


.320 


No. 5 


360 


.360 


No. 6 


400 


.400 


No. 7 


440 


.440 


No. 8 


480 


.480 


No. 9 


520 


.520 


No. 10 


5 6o 


.560 



Current in the Wire. The drop in the wire can- 
not be calculated by merely multiplying the main 



44 



ELECTRIC-WIRING, DIAGRAMS 



current by the various resistances of the various 
circuits given above. An examination of the circuit 
will show that the connecting wires of lamp No. i 
carry 10 amperes, while the connecting wires of 
lamp No. 2 carry 10 amperes and 9 amperes. This 
unequal distribution of current in the connecting 
wires which lead up to all of the lamps and the 
difference in drop in each lamp is shown in the 
following table : 



DISTRIBUTION OF CURRENT IN CONNECTING WIRES OF A SIMPLE 
10 LAMP CIRCUIT. 



Position of wire. 


Current 
in wire. 


Resistance 
of wire. 


Drop in 
volts. 


Between source and lamp No. i . . 
Between No. i and No. 2 


Amperes. 
10 


Ohm. 
.200 
.O4O 


2.OOO 
260 


Between No. 2 and No. 3 


8 


O4O 


o w ^ 

22O 


Between No. 3 and No. 4 


7 


.O4.O 


d*** 

.280 


Between No. 4 and No. 5. 


6 


O4O 


24O 


Between No. 5 and No. 6 


r 


O4O 


2OO 


Between No. 6 and No. 7 


4 


.O4O 


.160 


Between No. 7 and No. 8 


-i 


.O4.O 


.I2O 


Between No. 8 and No. 9 


2 


O4O 


.080 


Between No. 9 and No. 10 


I 


.OAO 


.O4O 











The last column of this table shows the drop 
due to the current and connecting wires of each 
lamp, but it does not show the total drop of the 
lamp. To illustrate, the first lamp has a drop of 
2 volts, because its connecting wires carry the full 



AND SWITCHBOARDS 45 

10 amperes and have a resistance of .2 ohm. The 
second lamp, however, is different ; its drop is 
greater, because it not only meets with the drop of 
the first lamp, but that of its connecting wires 
lying between lamps No. I and 2, equal to .36 volt. 
Lamp No. 2 therefore has a drop equal to 2.36 
volts, and lamp No. 3 will have a drop equal to 
lamp No. 2 plus the additional drop it experiences 
in its connecting wires lying between lamps No. 2 
and No. 3, amounting to .32 volt, or a total of 2.36 
-f- .32 = 2.68 volts drop for lamp No. 3. 

DROP OF EACH LAMP IN A SIMPLE 10 LAMP CIRCUIT, CURRENT 
10 AMPERES. SIZE OF WIRE, No. 10 B. & S. 



No. of 
lamp. 



Drop from source to lamp. 



Total 

drop in 

volts. 



I 
2 

3 
4 

I 

8 

9 

10 



Volts. 

2.00 2.000 

2.0O + .36 2.360 

2.00 + .36 + .32 | 2.680 

2.0O + .36 + .32 + .28 2.960 

2.00 + .36 + .32 +.28 +.24 ! 3.100 

2.00 + .36 + .32 + .28 + .24 + .20 I 3.400 

2. 00 + .36 + .32 +.28+.24+.20 + .I6 3-560 

2.00 + .36 + .32 + .28 +.24 + .20 + .I6 + .I2 3.680 

2. 00 + .36 + .32 + .28-J-.24 + .20 + .I6+.I2 -f .08 3-760 

2.oo + .36 + .32 +.28 + .24 + .20 + . 1 6 + .12 +.08 + .04 3.800 



It is of the utmost importance to carefully follow 
the items given in this table and their relation to 
the main facts. The table shows that in any cir- 
cuit of the character shown in the illustration the 
drop increases from the source to the last lamp. 



46 ELECTRIC-WIRING, DIAGRAMS 

Lamp No. i has a drop of 2 volts, lamp No. 10 a 
drop of 3.8 volts, and between these two occur in- 
creases in drop, due to the causes above specified. 

The purpose in view in making an analysis of 
wiring is to find the best methods to employ in 
laying out the circuits, for the purpose of keeping 
the drop as uniform as possible among the lamps. 
This task can only be accomplished intelligently 
and therefore economically, for the problem is as 
much commercial as scientific, by following cer- 
tain general principles in mapping out the most 
important circuits. 

The Wiedemann System. The purpose of the 
Wiedemann system (Fig. 6) was to connect each 




FIG. 6. Wiedemann System of Wiring. 

lamp in the system with an equal length of wire. 
By this means every lamp represented individually 
a circuit of equal resistance, and it was believed 
that the drop of each lamp would be alike. 

By following the length of circuit through each 
lamp in the sketch it will be seen that each lamp 



AND SWITCHBOARDS 4 7 

is supplied with current through 2,300 feet of No. 
10 wire. Take lamp No. I for instance, starting 
from the positive pole the current passes through 
1,000 feet of wire, then through the lamp, then 
through B, D, F, H, J, L, N, P (which are the 
connecting wires between lamp and lamp on one 
side of the circuit of 100 feet apiece) and finally 
through the indicated 500 feet of terminal wire. 
The total length met with for lamp No. I is there- 
fore 1,000 feet + 800 feet -(- 500 feet = 2,300 feet 
total. Tracing the circuit through lamp No. 2 will 
give i,ooo feet + A + D, F, H, J, L, N, P + 500 
feet == 1,000 + 100 + 700 -f 500 == 2,300 feet for 
lamp No. 2. Following the circuit through for each 
lamp will show exactly the same length of wire 
connected to each one. If there is the same length 
of the same size of wire connected to each lamp, 
the resistance in circuit with each lamp must be 
the same. The question now arising is this : Will 
the lamps have equal drop and therefore burn with 
equal candle power, or is the drop in the circuit 
of each lamp different? This question can be best 
answered by an investigation of the drop met with 
in the circuit of each lamp. To discover the drop 
in the circuit of each lamp, the resistance and cur- 
rent must be known. In the sketch the resistance 
is known, so the problem is reduced down to a 
statement of the number of amperes in each part 
of the circuit of each lamp. 

Amperes in Lamp Circuits. To find the am- 
peres in each lamp circuit refer to the sketch be- 



4 8 



ELECTRIC-WIRING, DIAGRAMS 



ginning with lamp No. i. Because every lamp has 
the two terminals of the circuit, respectively 1,000 
feet and 500 feet to consider alike, they will be 
left out of consideration for the present and par- 
ticular attention paid to the current in the con- 
necting wires met with in the circuit of each lamp. 
Following the 9 amperes along from the + pole it 
is seen that i ampere passes through lamp No. i 
and enters connecting wire B, leaving 8 amperes 
to pass through connecting wire A. Another am- 
pere passes through lamp No. 2 and enters con- 



Connecting wire. 


Amperes. 


Drop in volts. 


Positive wire. 






A 


8 


. X 8 = .8 


C 


7 


X 7 = -7 


E 


6 


. X 6 = .6 


G 


5 


X5 = -5 


I 


4 


. X 4 = 4 


K 


3 


X 3 = -3 


M 


2 


.1 X 2 = .2 





I 


.1 X I = .1 


Negative wire. 






B 


I 


. X i = .1 


D 


2 


. X 2 = .2 


F 


3 


X 3 = -3 


H 


4 


X 4 = -4 


J 


5 


X 5 = -5 


L 


6 


. X 6 = .6 


N 


7 


X 7 = -7 


P 


8 


.1 X 8 = .8 



AND SWITCHBOARDS 



49 



necting wire D, returning with the ampere from 
connecting wire B. The following table will clearly 
show the distribution of current in the connecting 
wire of the circuit. 

It is now a simple task to discover the drop met 
with in the circuit of each lamp. For instance, 
lamp No. I meets with a drop of .1 volt in B, .2 
volt in D, and in F, H, J, L, N, and P respectively, 
a drop of .3 + -4 + -5 + -6 + .7 + -8 volt or a total 
of 3.6 volts. Lamp No. I has its circuit through 
B, D, F, H, J, L, N, and P ; lamp No. 2 its circuit 
through A, D, F, H, J, L, N, and P, and lamps Nos. 
3, 4, 5, etc., as shown in the following table : 



No. of 
lamp. 


Circuit of lamp. 




Total drop of lamp. 


2 

3 

4 

6 

8 
9 


B, D, F,H, J, L, N, P. 
A, D, F, H, J, L, N, P. 
A, C, F, H, J, L, N, P. 
A, C, E, H, J, L, N, P. 
A, C, E, G, J, L, N, P. 
A,C, E, G, I, L, N, P. 
A, C, E,G, I, K, N, P. 
A, C,E,G, I, K,M,P. 
A, C,E,G, I, K,M,O 




.i+.2+. 3 +. 4 +.5+-6 + .7+-8 = 3-6 
.8+.2+. 3 +. 4 +.5+.6+.7+.8=4.3 
.8+.7+-3+-4+.5+.6+. 7 +.8=4.S 
.8+.7+.6+.4+.5+.6+.7+.8=5.i 
.8+.7+.6+.5+.5+.6+.7+.8=5.2 
.8 + . 7 +.6+.5+.4+.64-.7+.8=5.i 
.8+. 7 +.6+.5+. 4 +.3+. 7 4-.8=4.8 

.8+. 7 +.6 + .5+. 4 +.3+.2+.8=4.3 
.8+.7+.6 + -5+.4+.3+-2+.i=3-6 



According to the above data lamp No. 5 has the 
greatest drop and will therefore burn the dimmest. 
Its loss is 5.2 volts, then come lamps Nos. 4 and 
6 with a drop of 5.1 volts apiece, then lamps Nos. 
3 and 7 with an equal drop of 4.8 volts, lamps Nos. 
2 and 8 with 4.3 volts drop and finally lamps 



50 ELECTRIC-WIRING, DIAGRAMS 

Nos. i and 9 with equivalent drops in pressure 
of 3.6 volts. The middle lamps burn dimly, the 
ones on each side a little brighter, the lamps on 
each side of these a little brighter, etc. If the 
number of lamps arranged as shown in the sketch 
are even, the two middle ones will burn equally 
bright, the candle power increasing from these 
two in pairs equally to the two ends of the circuit. 
An experiment with a bank of 20 lamps connected 
up as shown on a no volt circuit will demonstrate 
the fall of candle power from the ends to the 
middle of the circuit. It is therefore evident that 
in the Wiedemann system although each lamp is 
in circuit with the same amount of resistance, be- 
cause the current is different in the connecting 
wires the drop of each lamp is different from its 
neighbor as shown. 

The Wiring Table. The manufacture of wire for 
electric light and power purposes has meant the 
utilization of a variety of wire gauges ; among 
which, the most important is the Brown and 
Sharpe, commonly indicated as the B. & S. gauge. 
These gauges differ from each other in their sizes 
and the circular mils corresponding to these sizes. 
If the B. & S. gauge is taken as the standard, all 
the sizes of wire in this particular gauge can be 
shown to arbitrarily arise from a consideration of 
the No. 10 size. This has approximately 10,400 
circular mils cross-section and a resistance of about 
i ohm per 1,000 feet. 

An examination of the B. & S. table will show 



AND SWITCHBOARDS 51 

the following interesting facts, of which practical 
use may be made in the development of a table 
for ready reference that will be almost identical 
with the wire manufacturers. In the first place, 
every three sizes of wire mean that the circular 
mils have either doubled or halved. For instance, 
a No. 10 wire, B. & S., has 10,380 circular mils; if 
a No. 7, which is three sizes larger, is compared, 
it is found to possess twice as many circular mils 
or 20,760. On the other hand, comparing a No. 
13 wire, which is three sizes smaller, only one-half 
the circular mils, or 5,190, are found. The same 
process can be carried on with respect to No. 10 
B. & S., for every size given in the regular wire 
table, such as Nos. 13, 16, 19, 22, etc., as well as 
Nos. 7, 4, 1,000, etc. 

It is well to know that the numbers correspond- 
ing to the different sizes of wire do not correspond 
numerically to the circular mils they represent. 
The circular mils of a wire diminish according to 
the table as the number of the wire increases. A 
No. o wire has more circular mils than a No. 10 ; 
or a No. 13 wire has less circular mils than a No. 
10, etc. These facts are best understood by a care- 
ful survey of the wire table as printed by the well- 
known manufacturers : 



ELECTRIC-WIRING, DIAGRAMS 



Gauge No. B. & S. 


Diameter in inches. 


Cross section. 
Circular mils. 


4-0 


0.4600 


211,600 


3-0 


0.4096 


167,800 


2 O 


0.3648 


133,100 


I O 


0.3249 


105,500 


I 


0.2893 


83,690 


2 


0.2576 


66,370 


3 


0.2294 


5 2 > 6 3 


4 


0.2043 


41,740 


5 


0.1819 


33>!oo 


6 


0.1620 


26,250 


7 


0.1443 


20,820 


8 


0.1285 


16,510 


9 


0.1144 


13,090 


10 


0.1019 


10,380 



The above figures give all sizes of wire as indi- 
cated from No. 10 B, & S. to No. 4-0, in other 
words, all of the larger sizes. According to the 
empirical rule just given No. 7 wire must have 
twice the circular mils of No. 10; No. 4 twice the 
circular mils of No. 7, etc., as shown below: 

No. 10 10,380 C. M., according to table. 

No. 7 twice No. 10 B. & S., or 20,760 C. M. 

No. 4 twice No. 76. &S.,or 41, 520 C. M. 

No. i twice No. 46. &S.,or 83,0400. M. 

No. 3 o . . .twice No. i B. & S., or 166,080 C. M. 



The intermediate sizes, such as the sizes that lie 
between No. 10 and No. 7, No. 7 and No. 4, etc., 



AND SWITCHBOARDS 



S3 



are found as follows: The difference in circular 
mils between No. 10 and No. 7 is 10,380 ; these are 
divided up equally between the three sizes, namely, 
Nos. 9, 8 and No. 7 gauge. Dividing this differ- 
ence into three parts gives 10,380 -=- 3 = 3,460 cir- 
cular mils. If 3,460 circular mils are added to No. 
10, No. 9 is obtained as shown below : 

No. 10 = 10,380 circular mils = 10,380 

No. 9 = 10,380 + 3,460 = 13,840 

No. 8 = 10,380 + (2 X 3,460) = 17,300 

No. 7 = 10,380 + (3 X 3,460) = 20,760 

This process must be followed out in arriving 
at the size of wire if the circular mils are given, 
or if a table is to be developed for practical pur- 
poses. The circular mils obtained by this method 
are such that they will show clearly the size re- 
quired. A comparison of the circular mils of the 
manufacturers' table and the above circular mils 
will demonstrate this fact. 



Regular wire table. 


Calculated sizes. 


Difference. 


No 10 


10 380 


No 10 


10 380 


O 

750 
790 
60 


No. Q.. 


. . 13,000 


No. Q . 


. . 1 3,84.0 


No. 8 


. 16,510 


No. 8 


17,300 


No. 7 


20,820 


No. 7 


20,760 











In spite of apparently large differences in area 
as shown by Nos. 9 and 8, between the regular 



54 



ELECTRIC-WIRING, DIAGRAMS 



table and the calculated sizes, the nearest sizes 
manufactured to those calculated are Nos. 9 and 8 
of the regular table. This removes any doubt of 
the practicability of the method. The other half of 
the table giving the sizes from No. 10 to No. 16, 
which are the lesser sizes, is subject to exactly the 
same rules : 



Gauge No. 
B.& S. 


Diameter in inches. 


Cross section in cir- 
cular mils. 


10 


0.1019 


10,380 


II 


0.09074 


8,324 


12 


0.08081 


6,530 


13 


0.07196 


5^78 


14 


0.06408 


4,107 


15 


0.05707 


3.257 


16 


0.05082 


2,583 



A point of difference arises, however, when size 
No. 13 is to be obtained from No. 10; in other 
words, when passing from a larger to a smaller 
size of wire. In this case the difference is to be 
subtracted instead of added. This means the recol- 
lection of the following rule : 

Rule. In passing from smaller to larger sizes 
of wire add the difference ; in passing from larger 
to smaller sizes of wire subtract the difference. 

To illustrate this fact, No. 10 wire differs from 
No. 13 wire as 10,380 circular mils differ from 5,190 
circular mils. This means that each intermediate 
size from No. 10 to No. 13 varies one-third of 5,190 



AND SWITCHBOARDS 



55 



circular mils or 1,730 circular mils from its neigh- 
bor as indicated below : 



Size wire. 



Circular mils. 



10 
II 
12 
13 



10,380 = 10,380 

10,380 - (J X 5,190) = 8,650 
10,380 (| X 5iiQo) = 6,920 
10,380 - (| X 5,190) = 5,190 



Although the size and circular mils are obtained 
very readily by a little practice with the above 
method, it is very important to know how to get 
the resistances as well. This is not any more 
difficult than the preceding, assuming a resistance 
of i ohm per 1,000 feet of No. 10 wire. As the re- 
sistance of a wire is inversely proportional to its 
cross-section in circular mils, a No. 13 wire which 
has 5,190 circular mils or one-half as much cross- 
section as a No. 10 would have twice the resist- 
ance per i ,000 feet or 2 ohms. A table can be 
constructed based on this principle as follows: 



Ratio of C. M. 


Size of wire. 


Circular mils. 


Resistance in 
ohms. 


I 


10 


10,380 


1.0000 


2 


7 


20,760 


.5000 


4 


4 


41,520 


.2500 


8 


i 


83,040 


.1250 


16 


3-o 


166,080 


.0625 



56 ELECTRIC-WIRING, DIAGRAMS 

The intermediate resistances are obtained by 
the same rule as that giving the circular mils. 
For instance, the resistance of a No. 9 and 8 is 
obtained by subtracting one-third of one-half of 
the difference in passing from the smaller sizes to 
the larger, and in adding one-third of one-half the 
difference in passing from the larger sizes to the 
smaller. 

If No. 10 has i ohm per 1,000 feet, then No. 7 
has .5 ohm per 1,000 feet and the difference is .5 
ohm. This difference is divided by 3, giving .1666 
ohm. In other words, the subtraction of .1666 ohm 
from No. 10 will give No. 9; subtracting .1666 
ohm from No. 9 will give No. 8, etc., as indicated 
below : 



Size wire. 


Resistance per i 


,000 feet. 


IO 


I 


= i.oooo 


9 


I .1666 


8334 


8 


i - (2 X .1666) 


= .6668 


7 


i - (3 X .1666) 


.5000 



For sizes which run the other way, that is, from 
a larger to a smaller size, addition is necessary. 
The following figures are correct in passing from 
No. 10 to No. 13 : 



AND SWITCHBOARDS 



57 



Size wire. 


Resistance per i 


,000 feet. 


10 


I.OOOO 


I.OOOO 


n 


i 4- (J X i) = 


I -3333 


12 


i + (I X i) - 


1.6666 


J 3 


i + (| X i) = 


2.000O 



By carefully following the method as described, 
entire independence of the regular wire table re- 
sults. It is possible to arrive at the size, circular 
mils and resistance of any wire by a short calcu- 
lation or a mental estimate, which not only saves 
time, but is an immense advantage to those em- 
ploying such principles as given as a means of daily 
livelihood. A few examples will show the appli- 
cation and value of the process in a simple wiring 
system : 

Example. What is the size and circular mils of 
the wire required to conduct 30 amperes over a 
350 foot run (Fig. 7) at a drop of 2 per cent., the 
pressure being no volts? 

The data is as follows : 



Drop 2.2 volts. 

Length of wire 700 feet. 

Amperes 30 

According to the formula: 

700 X 30 X ii 
C. M. = - - = 105,000. 



2.2 



ELECTRIC-WIRING, DIAGRAMS 



The practical question arising is this, what is 
the resistance per 1,000 feet and size corresponding 
to the answer? This is the method, starting from 
No. 10 B. & S. : 



DROP 2 PER CENT 



FIG. 7. Estimating Circular Mils and Size of Wire Without Wire 
Table for Reference. 



No. 10 10,380 

No. 7.'. 20,760 

No. 4 4i,5 20 

No. i 83 ,040 

No. 30 166,080 



c ohm per i ,000 feet. 
.5 ohm per 1,000 feet. 
. 2 50 ohm per i ,000 feet. 
.125 ohm peri ,000 feet. 
.0625 ohm per 1,000 feet. 



AND SWITCHBOARDS 59 

It is evidently between No. I and No. ooo, and 
if one-third of the difference is added, or 27,680 
circular mils, 110,720 are obtained corresponding 
to a No. o wire. The resistance of this size is .125 
ohm minus one-third of the difference in resist- 
ance between the two sizes. The resistance of 
1,000 feet of No. o wire is therefore approximately 
.1042 ohm. If 1,000 feet = .1042 ohm, then 700 
feet = .073 ohm. 

Applying the law .that E = C X R to check the 
answer, the drop is found to be 30 amperes X .073 
ohm = 2. 19 volts. 

In the above, the nearest size manufactured is 
No. o, and this size would have to be employed 
even though a difference of 5,000 circular mils 
existed. 




FIG. 8. 

Example. A power line is being run a distance 
of 500 feet (Fig. 8) to a 220 volt motor, taking 50 
amperes with a drop of 5 per cent., what is the size 
of wire, etc.? 

1,000 X 50 X n 
C. M. = = 50,000. 

No. 4 = 41,520. 
No. 3 = 55,360. 



6o 



ELECTRIC-WIRING, DIAGRAMS 



The nearest size is No. 3 B. & S. and the resist- 
ance is approximately .209 ohm per 1,000 feet. The 
drop is therefore .209X50=10.45 volts, a little 
short, but still to the advantage of the contractor. 
A table may be prepared which will save a great 
deal of time if properly used, in which the drop in 
volts per ampere per 1,000 feet is given as follows: 



Size wire. 



Drop in volts per 1,000 feet per ampere. 



10 

7 
4 
i 



I.OOOO 

.5000 
.2500 
.1250 
.0625 



Taking it the other way toward the smaller sizes 
the figures are in near approximation. 



Size wire. 


Drop in volts per 1,000 feet per ampere. 


IO 


I.OOOO 


13 
16 


2.0OOO 

4.0000 



The intermediate sizes and the drop correspond- 
ing to them on this basis would give a complete 
table as follows: 



AND SWITCHBOARDS 



61 



Size wire in 
B. & S. gauge. 


Volts drop per 1,000 
feet per ampere. 


Size wire in 
B. &S. gauge. 


Volts drop per i ,000 
feet per ampere. 


4 


05 2 3 


6 


.4166 


3-o 


.0625 


7 


.5000 


2 


0833 


8 


.6666 


I O 


.1041 


9 


.8333 


I 


.1250 


10 


I.OOOO 


2 


.1666 


ii 


J -3333 


3 


.2082 


12 


1.6666 


4 


.2500 


13 


2.0060 


5 


3333 


14 


2.6666 



Any number of simple problems in wiring can 
be worked out by means of this table, such as the 
following: If a circuit is to be installed to lose 
10 volts per 1,000 feet, carrying 30 amperes and 
a total drop of 50 volts, what is its size and length? 

The answer would be 5,000 feet of No. 5 B. & S. ; 
because a loss of 10 volts per 1,000 feet, with 30 
amperes, means a loss of .3333 of a volt per am- 
pere per 1,000 feet, corresponding to the size given 
above. 

The sketch (Fig. 9) shows the general idea dia- 



1000 FT. NO. 10 

7 
4 



DROP 1 VOLT PER AMPERE 



-'- M 



MQI 



WEIGHTS 
1 

4 
16 
64 



FIG. 9. Relative Lengths and Weights of Wire of Equal 
Resistance. 



62 ELECTRIC-WIRING, DIAGRAMS 



grammatically, also the relative weights of copper. 
This last item is of immense importance in con- 
nection with the drop, because in some cases 
where but little drop of voltage is very desirable 
the cost is prohibitive. The weight of copper re- 
quired to wire a building at 2 per cent, drop is 
exactly twice the amount required to wire a build- 
ing at 4 per cent. drop. The saving in copper, by 
using a higher pressure, is apparent from the 
following figures : 

DISTANCE 500 FEET WATTS = 10,000, DROP 5 PER CENT. 



Size. 


Volts. 


Amperes. 


Circular 
mils. 


Relative weight 
of copper. 


40 


IOO 


IOO 


2li,6oo 


32 


i o 


2OO 


50 


105,800 


16 


3 


400 


25 


52,900 


8 


6 


800 


12.5 


26,450 


4 


9 


1600 


6.2 5 


13^25 


2 


12 


3200 


3-125 


6,612 


I 



This relates more particularly to power trans- 
mission but is very instructive in showing how the 
choice of wire, as regards its size, is greatly de- 
pendent upon the policy pursued in planning the 
installation. 



AND SWITCHBOARDS 63 



CHAPTER III 

ELEMENTS OF A WIRING SYSTEM. MEANING OF MAINS, 
FEEDERS, BRANCHES. PROPORTIONING THE DROP IN 
THE VARIOUS PARTS OF THE SYSTEM. THE CENTER OF 
DISTRIBUTION. EXAMPLES OF THE EFFECTS OF DROP 
IN PARTS OF THE CIRCUIT. EQUALIZING THE PRESSURE. 
DYNAMOS FOR INCANDESCENT LIGHTING. EFFECTS 
OF CHANGES IN THE FIELD OF DYNAMOS UPON THE 
LIGHTING. A WIRING SYSTEM WITH FOUR CENTERS OF 
DISTRIBUTION. THE LIFE OF A LAMP. 

Elements of a Wiring System. The analysis of 
a x wiring system discloses three fundamental ele- 
ments (Fig. 10), called mains, feeders and branches. 
These parts are subject to the same calculation for 
the discovery of the drop taking place in them as 
any simple circuit previously described. In laying 
out a wiring system these elements must be care- 
fully considered and a great deal of discretion is 
necessary in making allowance for the distribution 
of the total drop in each part. If, for instance, the 
total drop is 10 volts, and this is to be divided up 
between the elements above mentioned, the aver- 
age drop in mains, feeders, and branches would be 
3-333 volts. But there is no fixed rule for this con- 
clusion and the drop in the elements of a wiring 
system must be left largely to the judgment and 



6 4 ELECTRIC-WIRING, DIAGRAMS 

experience of the contractor. To the contractor 
such questions arise in connection with this fact as : 
What is the cost of copper? What is the cost of 
labor? The labor question is by far the most im- 
portant one, because it would be easy to show by 
comparing the cost of materials included under the 
head of mains, feeders and branches as well as the 
moulding or tubing in which they would be laid 
with the cost of labor in installing them, that 
labor is of the first importance. One hundred 
dollars worth of materials may cost anywhere 
from $50 to $200 or more to install. It would be 
difficult indeed to attempt to give iron-clad rules 
for determining these relationships, but perhaps 
the best that can be done is to follow the common- 
sense rule of laying out the work so that the labor 
bill is low. Where it is possible to have a greater 
drop, and, consequently a lighter wire, and in 
some cases less labor in handling it, the choice 
becomes self-evident. W r hen the cost of labor is 
equal in both cases, saving can only be attempted 
with the copper and the reverse, namely, when the 
cost of copper is equal in both cases saving must 
be attempted in the labor. Perhaps this idea can 
be best illustrated by a practical case (Fig. n). 
Suppose 100 amperes are to be supplied to a set 
of feeders and branches, will it be necessary to use 
one or two pair of mains? If the wires are to be 
laid in moulding and run a distance of 100 feet, a 
calculation will show the size of wire required. 
According to the method a knowledge of the drop 



AND SWITCHBOARDS 65 

to take place in the mains is necessary. If the en- 
tire drop is 3 per cent., an arbitrary choice of I per 
cent, can be considered, which at the usual voltage 
of no would mean i.i volts. The circular mils 
required are then 100 X 200 X n -r- i.i = 200,000, 
corresponding to a No. 4 o wire whose diameter is 
.4600 of an inch. If the wires are run straight 
ahead there is a possibility of using such a heavy 
wire but where there are bends, it is much more 
advisable to run two mains of 100,000 circular mils 
apiece or about No. o wire. This is true where 
moulding is used, although many might raise objec- 
tions to this conclusion on the grounds that it costs 
less to run a single line of 200,000 circular mils than 
two lines of 100,000 circular mils apiece. This mat- 
ter can only be decided by experience and even then 
a decision would rest largely upon the character of 
labor employed, which naturally involves questions 
of strength, skill and speed in the performance of 
duties. 

If a single line of 200,000 circular mils is in- 
stalled there is a saving in cost of material and 
labor, provided it takes less time to run the wires. 
A flexible cable might be employed and labor 
saved, but the wire costs more, so the point to be 
considered of cost of wire or material and cost of 
labor is in a practical sense a part of the triple 
question involved under the head of drop, material 
and labor. 

The arbitrary choice of I per cent, for the drop 
in the mains might have been made 2 per cent. ; 



66 



ELECTRIC-WIRING, DIAGRAMS 



in which case the size of wire being one-half or 
100,000 circular mils, the doubt disappears ; but 
only i per cent, drop is left, and it is imperative to 
divide this up between the feeders and branches. 
If, putting the copper here, means more labor dis- 
tributed among a variety of wires, than putting it 
on the mains, then this is where less drop is most 
expensive. In the following sketch the elements 
of a wiring system are shown : 



*TJ DYNAM 



'' 



FIG. 10. Elements of a Wiring System. 

In some cases the wires rising through the build- 
ing are called " risers," which would give four ele- 
ments instead of three, called mains, risers, feeders 
and branches. If the number of amperes are not 
too great the above system is satisfactory as in the 



AND SWITCHBOARDS 67 

case of a small factory. Where it is necessary to 
conduct a heavy current to each floor of a build- 
ing the design is changed in this respect ; the num- 
ber of risers are increased. It is likely in such a 
case, the number of feeders are also increased, 





FEEDER 


1 




] 












BRANCH 




J 




FEEDER 






1 










BRANCH 

| 




| 




FEEDER 






1 




1 


BRANCH 1 





100 AMPERES 



100 AMPERES 



FIG. ii. System with Individual Mains. 



and in all probability the number of branches. 
But the difference is only in degree, that is to say, 
the new design would merely be a repetition of 
the last sketch. A case like this would arise where 
about 100 amperes are to be used on each floor of 
a three-story building, as shown in the above illus- 
tration : 

The foregoing sketches become very elaborate 
when a large structure is to be wired and every 



68 ELECTRIC-WIRING, DIAGRAMS 

circuit is shown in the drawing. In many cases 
where the total drop is very small, for instance, 2 
per cent., it is very difficult to divide the drop up 
between the various parts of the system in a 
scientific manner. The fact of greatest importance 
is this : that if a certain drop takes place in a build- 
ing it is due to a certain resistance and a certain 
current. Although more copper may be used in 
one part than another, it is evident that the sum 
total of copper will remain the same although its 
disposition will change. It is a good policy to make 
an allowance for overload in the mains and risers, 
in which case the drop will be less in the mains 
than any other part of the circuit in proportion to 
the rest. If for instance 2 per cent, is to be lost in 
drop and only J of I per cent, in the mains, this 
would leave i^ per cent, for the rest of the circuit. 
Calculation will show how the sizes of wires would 
vary under these circumstances. The circular mils 
of the mains, risers, feeders and branches, on the 
basis of one estimate, can be compared with the 
circular mils estimated on a different basis, that 
is, a different arrangement of the percentages of 
drop equal to the total allowed. The following 
case is of interest in illustrating this idea : 

Example. What sizes of wire are required to 
equip a building for electric lighting at no volts 
pressure, with a 3 per cent, drop, consisting of two 
floors (Fig. 12) taking 50 amperes apiece; the 
length of mains 50 feet, length of feeders 50 feet, 
and length of branches 25 feet. 



AND SWITCHBOARDS 



69 



FEEDER 50 FT. 



BRANCHES 25 FT. , 
10 AMPERES 



FEEDER 50 FT. 



FIG. 12. Wiring System for Two Floors. 

The total drop is 3.3 volts, which may be divided 
up between the three elements equally for trial 
figures and for purposes of comparison as follows: 

Mains 100 feet wire, mains i.i volts drop, mains 
100 amperes: 

100 X 100 X ii 

C. M. = - = 100,000. 

i.i 

Feeders 100 feet wire, feeders i.i volts drop, 
feeders 50 amperes : 

100 X 50 X ii 
C. M. = - - = 50,000. 

Branches 50 feet wire, branches i.i volts drop, 
branches 10 amperes : 



70 ELECTRIC-WIRING, DIAGRAMS 



CM. 



50 X 10 X ii 



= 5>ooo. 



Arranging this data in the form of a table will 
show more clearly the comparison referred to and 
will embrace all conditions of drop, high and low, 
for each element of the circuit : 



Per cent, drop 
in volts. 


Mains 100 feet. 
Circular mils. 


Feeders 100 feet. 
Circular mils. 


Branches 
50 feet. 
Circular mils. 


.1 


1,100,000 


520,000 


55,000 


.2 


520,000 


260,000 


27,500 


-3 


366,667 


*73,333 


i8,333 


4 


275,000 


130,000 


J 3>75o 


5 


220,000 


104,000 


1 1 ,000 


.6 


183,334 


86,667 


9,166 


7 


157^43 


74,285 


7,857 


.8 


137.500 


65,000 


6,875 


9 


122,222 


57.777 


6,ni 


I.O 


IIO,OOO 


52,000 


5,5oo 



If possible a table of this character should be 
drawn up for the various important parts of a wir- 
ing system as it will enable an accurate idea to 
be gained of the size and cost of installation as the 
percentage of drop in each element is modified. 

In the previous example the drop is equally 
divided between the elements constituting the cir- 
cuit. If this is not the case the results may be 
tabulated for convenience and comparison as be- 
fore. As will be observed the total drop according 



AND SWITCHBOARDS 



to the figures is the total allowed, namely, 3.3 volts. 
All the data is obtained from the last table : 

COMPARATIVE TABLE. 





Drop. 


Circular 

mils. 


Size 
wire. 


Mains 


. r 


220 ooo 


n 


Feeders 


j 
I O 


r 2 OOO 


*J 


Branches 


i 8 


J^jVA-AJ 

3OC C 




Mains 


I O 


>55 


1 5 


Feeders 


c 


104 ooo 




Branches 


J 

i 8 


3OC C 




Mains 


J I 


U 55 

TOO OOO 


*:> 


Feeders 


J J 






Branches 


I.I 


^)U,UUU 

5 ooo 


3 

T 7 








1 3 



A choice of wires is presented with which the 
wiring can be successfully accomplished. The first 
results in the table cannot be used because they 
call for the use of a 4 o wire. The second set of 
results are fairly uniform with the exception of the 
No. 15 wire, which is too small and forbidden by 
the Fire Underwriters. The last set of results are 
more satisfactory yet capable of further rearrange- 
ment to get the correct result. If it is possible to 
obtain a fair degree of uniformity in the sizes of 
wire a great advantage is gained as moulding or 
tubing can be bought to correspond and the work 
is, in a sense, simplified. 



72 ELECTRIC-WIRING, DIAGRAMS 

Center of Distribution. In laying out a wiring 
system, one of the most important features is the 
selection of the center, or centers, of distribution. 
A wiring system is in many respects like a nervous 
system in its branches and ramifications, but the 
most interesting fact is the similarity between the 
ganglions in the nervous system and the centers 
of distribution in the wiring system. From these 
points, not only does the current become distrib- 
uted, but the pressure is delivered as nearly uni- 
form as possible to the various lamps or outlets 
at which it is utilized. An examination of the 
wiring of a large building discloses the fact that 
at one or more points on the floor, panel boards 
are in use, from which many lines run to lamps, 
or groups of lamps on the same floor. In smaller 
buildings the distribution may be different. One 
panel board may suffice for more than one floor, 
or, in other words, the centers of distribution are 
fewer, because the demand for current at given 
points is less. 

Example. A single case may serve to illustrate 
the advantage gained by choosing a center or 
centers of distribution so far as the question of 
drop is concerned. Suppose a line 1,000 feet long 
consisting of No. 10 wire is supplied with current 
at no volts pressure and 10 lamps are to be lit at 
each end of the line ; which is the best way of feed- 
ing current to the line so as to keep the drop at a 
minimum? If the current is supplied from one end, 
the drop would be C X R = current of 20 lamps X 



AND SWITCHBOARDS 73 

resistance of 2,000 feet of No. 10 wire =10X2 = 
20 volts. According to these figures the lamps 
nearest to the point at which the current enters 
would receive no volts minus 10 volts or 100 volts, 
and the lamps at the distant end 1,000 feet away 
would receive 10 volts less or only 90 volts. This 
would mean a heavy reduction in candle power 
and the failure of the plan as a successful wiring 
system. On the other hand, supposing the current 
is fed into the middle of the line, making this the 
center of distribution instead of the end, the con- 
ditions would then be different and the drop greatly 
reduced. Under these circumstances the current 
travels from the middle of the circuit 500 feet to 
each end of the line. The drop for each group of 
10 lamps at either end of the line is then equal to : 
Current of 10 lamps X resistance of 1,000 feet of No. 
10 wire = 5 X i = 5 volts drop. This means a great 
reduction in the drop for the lamps, uniformity of 
pressure for the lamps, and a much more efficient 
use of the copper employed in the line. If, instead 
of feeding into the middle of this 1,000 foot circuit, 
two lines or feeders are run 250 feet away from the 
ends, the drop for each group of lamps becomes : 
Current of 10 lamps X resistance of 500 feet of wire 
= 5 amperes X 2 ohm = 2.5 volts drop. 

The above figures are instructive in showing how 
the point or points from which the current is dis- 
tributed will influence the light or drop of the 
lamps. The following table indicates the effect of 
these changes : 



74 



ELECTRIC-WIRING, DIAGRAMS 







Length of 


Am- 


Drop 


Ohms. 




No. 10 wire. 




in 






Feet. 


peres. 


volts. 


2 


Feeding at one end 


2,OOO 


IO 


2O 












I 


Feeding at middle 


I OOO 


r 


r 












* 


Feeding at J from end 


666 


5 


3-333 


i 


Feeding at \ from end 


500 


5 


2.500 



This idea is of the utmost value in street rail- 
way work, which in many respects possesses all 
the qualifications of a wiring system. The trolley 
wire is one leg of the circuit and the tracks the 
other, and between the positive and negative wires 
thus indicated, instead of lamps, as in the system 
of incandescent light wiring, trolley cars are run- 
ning. The current these cars take is the cause of 
a heavy drop on the line, which is to a large extent 
reduced by connecting into the line at definite 
points, feeders which supply both current and 
pressure where it is most necessary. By this 
means, a comparatively uniform pressure is pre- 
served throughout the line under all conditions of 
load. 

Equalizing the Pressure. The choice of centers 
of distribution is for the purpose, as previously ex- 
plained, of equalizing the pressure. In house wir- 
ing, apartment houses and hotels particularly, dif- 
ferences in the illuminating power of lamps is 
prohibitive. It is necessary to use many centers 
of distribution to accomplish this object. In the 



AND SWITCHBOARDS 



75 



following sketches (Figs. 13, 14 and 15) may be 
seen the development of this idea, as illustrated by 



CENTEITOF CIS' 


UTION 




~ 




CENTER OF 1 


RIBUTION 








( ) 


i 


*> 


L 


fl 



FIG. 13. One Center of 
Distribution. 



FIG. 14. Two Centers 
of Distribution. 



76 ELECTRIC-WIRING, DIAGRAMS 



the case of one, two, three and more centers of 
distribution. 



CENTER OF D T 



CENTER OF DISTF IBUTION 



a 



CENTER OFDI JTRIBUTION' 




LJ 



FIG. 15. Three Centers of Distribution. 



AND SWITCHBOARDS 77 

Sub-centers of Distribution. The main centers 
of distribution are of first importance in laying 
out the wiring system, but then come the second 
or sub-centers of distribution (Fig. 17), which are 
the means of transmitting the power to the lamps, 
etc., at approximately the pressure of the main 
centers of distribution. The same phraseology 
might be aptly applied with reference to mains, 
feeders, branches, etc., calling those which perform 
the same function in a secondary sense, sub-mains, 
sub-feeders, sub-branches, etc. The problem of dis- 
tributing the drop in the various elements of such 
a system in a practical, economical and scientific 
manner becomes a more difficult task as the various 
complexities of the system increase. The principle 
must be rigidly adhered to of calculating the drop 
for every line and part of the circuit, so that the 
total drop does not exceed the amount allowed for 
in the specifications. As a general rule the mis- 
take is made of not estimating the total drop from 
the source of supply through the circuit to the 
lamps it ends in as shown by the following simple 
sketch (Fig. 16) illustrating this important point 
in the calculation of wiring: 



ELECTRIC-WIRING, DIAGRAMS 




FIG. 1 6. Wiring Diagram Showing the Drop Limited 
to Two Volts. 

The drop frorrLthe source of supply to any group 
of lamps does not exceed 2 volts, as shown by trac- 
ing the circuit from the switch to the center of dis- 
tribution. 

From the switch through E to C = 2 volts. 
From the switch through F to A = 2 volts. 
From the switch through F to B = 2 volts. 
From the switch through F to G = 2 volts. 
From the switch through E to H = 2 volts. 
From the switch through E to D = 2 volts. 

The limit of 2 per cent, need not be observed so 
carefully in houses or buildings with their own 
generating plant. In such cases the pressure may 
drop 4 or 5 volts without any inconvenience on ac- 



AND SWITCHBOARDS 79 

count of the character of the dynamo installed and 
the extra pressure generated to obviate this diffi- 
culty. 

Dynamos for Incandescent Lighting. The class 
of dynamos employed for incandescent lighting are 
called shunt wound and compound wound. The 
shunt wound dynamo can produce a rise or fall in 
pressure by field regulation. In order to grasp this 
fact it is necessary to understand the fundamental 
principle relating to the generation of electromotive 
force, which may be popularly expressed in the fol- 
lowing words: Electromotive force is developed 
by a certain motion of conductors in a magnetic 
field or a certain motion of lines of force through 
a conductor. In other words, electromotive force 
is developed in a dynamo by motion, magnetism 
and conductors. A very simple formula expresses 
the relationship between these elements, based upon 
the manner in which a volt is generated. 

A volt is generated by the cutting of 100 million 
lines of force in one second. The formula is con- 
structed with the idea of giving the correct answer 
with any number of conductors, with any degree 
of motion and with any number of lines of force. 

Formula for calculating the EMF. of a dynamo: 
The electromotive force is equal to the revolutions 
of the armature per second X the number of con- 
ductors on the armature X the number of lines of 
force passing through the armature, or 
E M F = speed per second X lines of force X conductors 

100 million. 



8o 



ELECTRIC-WIRING, DIAGRAMS 



It is expressed in symbols in the following form : 
E = NXcXn-=- 100,000,000 where N = lines of 
force, c = conductors and n = speed per second in 
revolutions. 



CENTER CF DISTRIBUTION 
~C.O. 




FIG. 17. Four Main Centers of Distribution and Sub-centers. 

The entire purpose of this analysis is to show 
what a shunt machine is, and how it regulates its 
pressure, so that its relative importance to the 
wiring of a building and the lighting may be better 



AND SWITCHBOARDS 



81 



understood. The EMF. may be increased or dimin- 
ished by increasing or diminishing 1 the conductors 
on the armature, the strength of field or the revo- 
lutions per second. As a general rule, the lines of 
force are increased or diminished to produce cor- 
responding changes in the EMF. This is accom- 
plished by using a device called a resistance box 
connected in circuit with the winding of the mag- 
nets. If the handle of this box is turned one way 
or the other, the current is controlled, increased 
or diminished, and thus affects the power of the 
magnets, strengthening them or weakening them 
accordingly. If the dynamo must develop more 
pressure, the magnets are made to develop more 
magnetism by increasing the current passing 
through them, or vice versa. 

The meaning of this formula is best understood 
by developing a table showing with what combina- 
tions of magnetism, speed and conductors no volts 
can be generated in a dynamo : 



Revolutions 
per second. 


Conductors. 


Lines of force. 


Volts. 


IOO 


1 10 


1,000,000 


no 


50 


HO 


2,000,000 


no 


50 


55 


4,000,000 


no 


25 


55 


8,000,000 


no 


12.5 


55 


16,000,000 


no 


25 


27-5 


16,000,000 


IIO 


IO 


55 


20,000,000 


no 



82 ELECTRIC-WIRING, DIAGRAMS 



Taking the above figures as a basis for estimat- 
ing, the EMF. could be held constant while an in- 
finite variety of combinations would be possible in 
producing the same result. The lines of force are 
shown to vary from 1,000,000 to 20,000,000, with 
corresponding changes in the speed and conductors, 
thus passing from the class of machines called high 
speed to another class called slow speed generators. 
If the first line of figures is examined, the speed 
is indicated as 6,000 revolutions per minute and 1 10 
conductors ; to produce i volt additional at the same 
speed additional lines of force equal to 1,000,000 -r- 
no or 9.091 are required. In other words, any 
change of pressure taking place in a dynamo, if not 
produced by a change in the speed or conductors 
is conveniently produced by a variation in the 
number of lines of force supplied to the armature. 

In the following table the changes in magnetic 
field required to produce a change of five volts in 
the pressure are shown with the speed and con- 
ductors constant : 

TABLE SHOWING CHANGES IN VOLTS THROUGH CHANGES IN FIELD. 



Extra 
volts. 


Revolutions 
per minute. 


Conduc- 
tors. 


Field strength. 


Volts. 


O 


6,OOO 


no 


I,OOO,OOO 


no 


I 


6,000 


no 


1,009,091 


in 


2 


6,OOO 


no 


I,0l8,l82 


112 


3 


6,OOO 


no 


1,027,273 


"3 


4 


6,OOO 


no 


1,036,364 


114 


5 


6,OOO 


no 


1,045,455 


n5 



AND SWITCHBOARDS 83 

The resistance box connected to the field coils, 
as above mentioned, will therefore be the means of 
increasing the dynamos EMF., but not necessarily 
the pressure it sends out. If the armature of a 
dynamo is regarded as part of a wiring system it is 
quite evident that, like any other conductor, an 
increase of current will mean an increase of drop. 
This being the case, the dynamo loses its own 
pressure as it is called upon for more and more 
current, so that if its original pressure was no 
volts, with only one lamp in circuit its pressure 
would be considerably lower at one-quarter, one- 
half and full load. The drop in the armature is 
not the only influence at work tending to lower the 
pressure of the dynamo. As the armature carries 
more current it becomes a stronger and stronger 
electro-magnet whose action upon the field in which 
it spins around is destructive. It reduces it sys- 
tematically and so effectively, that if external means 
were not employed to compensate for this phenom- 
enon, electric lighting would become a difficult, if 
not an impossible task on a commercial scale. In 
shunt wound dynamos the regulation of pressure 
is accomplished by varying the field in the manner 
described and this obviates the evil effects of drop 
in the armature due to its resistance and the cur- 
rent it carries and the magnetic armature reaction 
which also takes place. But to regulate in this 
manner it is necessary to be in constant attendance 
upon the dynamo, unless some assurance is made 
that the changes in load will not take place rapidly, 



84 ELECTRIC-WIRING, DIAGRAMS 

or unless the dynamo is of immense proportions 
and its armature, therefore, of such low resistance, 
that an increase of hundreds of amperes must oc- 
cur before any severe drop is felt. Regulation of 
pressure can be carried out practically and auto- 
matically by means of automatic dynamos called 
compound wound dynamos. These machines are so 
constructed, particularly their winding, that when 
the two losses, of drop and armature reaction take 
place, the dynamo automatically increases its own 
strength of field without the aid of any resistance 
box. A treatise on wiring is hardly the place to 
go into the technical features of dynamo construc- 
tion, except so far as they relate to the main point, 
the wiring problem ; but it is evident that the wir- 
ing problem is to a large extent the problem of 
electric lighting, and this in itself calls for a thor- 
ough understanding of the differences in purpose 
of construction and operation of the generators 
employed. In the compound wound dynamos, to 
briefly conclude this explanation, the regulation is 
automatically accomplished by sending the main 
current around the field coils so that as this current 
increases or diminishes the strength of the mag- 
nets it circulates around, will also increase or 
diminish, and consequently the dynamos will pro- 
duce more volts only when the armature produces 
more current. 

It is of the utmost importance to remember that 
the shunt wound and compound wound dynamos 
are used for central station, street railway and pri- 



AND SWITCHBOARDS 85 

vate plants all over the United States for the 
generation of direct current. Many changes have 
taken place, so that the above statement does not 
hold true for all cases, or for the most modern 
plants. It does hold true, however, for such plants 
as are installed in public buildings, hotels, apart- 
ment houses, etc. The large station of the Edison 
Company at Pearl and Elm streets, New York, has 
several big generators, shunt wound, with resist- 
ance boxes in use for regulation in operation there. 
The wiring of buildings calls for a consideration 
of the above facts so that provision can be made 
in the distribution of the drop for the higher and 
lower pressure in the upper and lower parts of it. 
For instance, if a no volt generator is installed, of 
the automatic type, and it is over compounded, 
this means that it may produce 115 volts at one- 
quarter or one-half load, and then fall slightly as 
the load increases to 112 volts or a trifle more or 
less. In this case, considerable drop can be pro- 
vided for in the wiring of the lower half of the 
building. Where provision is ordinarily made for 
a drop limited to two volts, at least twice that drop 
can now be experienced with a corresponding sav- 
ing in copper in wiring the lower part of the 
structure. 

The resistances of the various mains, feeders and 
branches must be carefully calculated in conse- 
quence of this in order that the drop takes place, 
otherwise the lamps will deteriorate rapidly through 
excess pressure. Incandescent lamps are built to 



86 ELECTRIC-WIRING, DIAGRAMS 

give a certain candle power with a certain terminal 
pressure applied. If this pressure is too great the 
current increases to such a point that the life of 
the lamp is endangered by the overheating of the 
filament. The filament loses its resistance as it is 
heated. A 16 cp. no volt lamp cold has a resist- 
ance of about 450 ohms ; when it is incandescent 
its resistance is about 225 ohms. As the filament 
is heated more and more its resistance becomes 
greatly reduced and five or ten more volts than 
the lamp is supposed to take greatly increases the 
current, the temperature and the light, and cuts 
down the period of usefulness. About 600 or 700 
hours, represents the effective light-giving period. 
It may, of course, be made to last much longer by 
keeping the pressure down below its proper value, 
but while the life of the lamp is increased the cost 
of the light produced in this manner is very heavy 
as compared with the cost at the correct pressure. 
A few figures will illustrate this point clearly. If 
it costs $5,000 a year to produce 50,000 cp. in a 
building, including wages, depreciation of machin- 
ery, coal, etc., and the engineer tries to save the 
lamps by running the pressure low, he probably 
cuts down the light 25 per cent, although full candle 
power is paid for. He saves an annual expense for 
new lamps of about $600, but throws away, so to 
speak, $1,250 worth of light. Lighting under these 
circumstances is a failure, giving no satisfaction 
for the money invested and represents the worst 
phase of false economy. 



AND SWITCHBOARDS 87 



CHAPTER IV 

MEASUREMENT OF RESISTANCE. PRINCIPLE OF THE WHEAT- 
STONE BRIDGE. BALANCING THE RESISTANCE OF FOUR 
LAMPS. MEASURING A LAMP HOT AND COLD. MEASUR- 
ING INSULATION RESISTANCE. THE INSULATION RE- 
SISTANCE OF BUILDINGS WIRED FOR ELECTRIC LIGHT- 
ING. THE THREE WIRE SYSTEM COMPARED WITH THE 
TWO WIRE. CALCULATING THE THREE WIRE SYSTEM 
OF WIRING. CIRCUITS OF A THREE WIRE SYSTEM 
WITH TWO CENTERS OF DISTRIBUTION. CALCULATION 
OF POUNDS OF COPPER FOR MAINS OR FEEDERS. 

THE laying out of circuits in many respects com- 
prises all that may be said about electric wiring, 
with the exception of a recognition of those prin- 
ciples which include a practical knowledge of the 
measurement of resistance. The measurement of 
resistance is not limited to the measurement of the 
metallic resistance, but includes the insulation re- 
sistance as well. To measure any resistance calls 
for a knowledge of the fundamental principle in- 
volved in the theory and operation of the Wheat- 
stone Bridge. 

The Wheatstone Bridge. The Wheatstone 

Bridge is employed for the measurement of resist- 
ance and consists of a kite shaped arrangement of 
resistances in which each arm of the kite or bridge 



88 



ELECTRIC-WIRING, DIAGRAMS 



is a different resistance. In order to grasp the true 
significance of this device, a brief review of the 
situation with regard to resistances in multiple 
must be considered. According to KirchofFs law, 
the total resistance of any number of resistances 
in multiple can be readily calculated. Not only is 
the resistance estimated, but the current in each 
branch, and consequently the drop, is readily cal- 
culated. 

In the following sketches (Figs. 18, 19 and 20) 
the resistance and current are given ; consequently 




FIG. 18. Current in Each Branch. 




12 VOLTS 

o o 



FIG. 19. Resistance of Each Branch. 



AND SWITCHBOARDS 



89 



the drop in each branch is 12 volts respectively; 
that is to say, the application of 12 volts to a re- 
sistance of 2, 4 and 6 ohms, would mean a current 
of 6, 3 and 2 amperes and a drop in each circuit of 
12 volts. Such being the case, the investigation 
of the conditions that exist in a circuit composed 
of resistances forming loops in multiple is similar 
in many respects to the conditions that exist in a 
Wheatstone Bridge. 




FIG. 20. Drop in Each Branch. 

In a Wheatstone Bridge there are two resistances 
in multiple connected across by a galvanometer 
or some instrument of equivalent delicacy which 
indicates the existence of certain conditions. These 
conditions can only exist when the resistances bear 
a certain numerical relationship to each other. The 
relationship is simple and instructive and can be 
expressed by the conventional formula A : B as 
C : D, when A, B, C and D represent the four re- 
sistances obtained by connecting across the loop 
by a galvanometer as shown in Fig. 21. 



90 ELECTRIC-WIRING, DIAGRAMS 

The real meaning of this remarkable relationship 
is, that when the ratio of A to B is the same as 
the ratio of C to D no current passes through the 




FIG. 21. Wheatstone Bridge Obtained by Connecting Across with 
Galvanometer. 

galvanometer circuit and the bridge is said to be 
balanced. The explanation of the effect of this in- 
teresting condition is to be found in a careful ex- 
amination of the various drops occurring in the 
different parts of the circuit designated at A, B, C 
and D. If values are given to the resistances (Fig. 
22) comprising the respective parts of the Wheat- 
stone Bridge as shown, the following conditions 
exist : 

Arm A drop 50 ohms X i ampere =25 volts. 
Arm B drop 100 ohms X J ampere =25 volts. 
Arm C drop 150 ohms X \ ampere =75 volts. 
Arm D drop 300 ohms X i ampere =75 volts. 



AND SWITCHBOARDS 91 

In other words, an examination of the theory 
and practice of the Wheatstone Bridge is merely 
an examination of the principles underlying the 
theory and practice of electric wiring. In the illus- 
tration it is shown that the points to which the 
galvanometer is connected are points at which the 
drop is equal and it follows that these are the only 
points in the circuit at which the galvanometer will 

1/2 AMPERE 




FIG. 22. Calculating the Drop in a Bridge. 

remain at rest. It is therefore only necessary to 
provide a current and resistance at those points 
at which the galvanometer is connected whose 
product is equal at each end and the measurement 
of resistance becomes a practical possibility. 

In the practical application of the Wheatstone 
Bridge for the measurement of resistance the three 
arms as they are called, A, B and C, are utilized as 



92 ELECTRIC-WIRING, DIAGRAMS 

follows : A and B are adjusted to a fixed ratio such 
as 1:2, i : 10 or 10: 1,000, etc. C is then manipu- 
lated until a balance is struck, that is, until the gal- 
vanometer or indicating instrument is at rest. The 
conditions that then exist are that the arms express 
the ratio of A : B as C : D. In such a case as this 
D is the resistance to be found and it can only be 
found by balancing the bridge. To balance the 
bridge the unknown resistance is inserted in that 
part representing the D arm, and when the correct 
ratro is established the process is completed. The 
resistance of fields, armatures and other circuits is 
readily measured by means of the " Bridge " with 
an accuracy that is without its parallel in other 
allied sciences. 

One of the most instructing of experiments is 
that of constructing a Wheatstone Bridge of incan- 
descent lamps (Fig. 23) and noting the fact that 




FIG. 23. Bridge of Incandescent Lamps, Middle Lamp Will Not 
Burn. 



AND SWITCHBOARDS 93 

when the lamps in the four arms are burning the 
middle lamp will not burn. 

The entire situation can therefore be summed 
up in a word, that the drop must be equal in the A 
and B arms and the indicator or galvanometer will 
be at rest, and in order to secure this condition of 
affairs the resistances of the different arms must 
express the ratio of A : B as C : D. 

Examples. If the A arm is 10 ohms, the B arm 
100 ohms, and the C arm 99.9 ohms, what is the 
D arm ? According to the ratio D = BXC-=-A = 
loo X 99-9 -f- 10 = 999 ohms. Or the problem may 
be given in this form : The resistance of a tele- 
graph line is to be measured ; the A and B arms 
are set at the ratio of 10 to 1,000, the telegraph 
line consists of two loops of equal length and resist- 
ance, if the C arm causes a balance when it is 5 
ohms, what is the resistance of each loop of the 
telegraph line? Applying the formula D = i.ooo X 
5-^10 = 500 ohms ; but D = the resistance of two 
loops in multiple, therefore each loop is equal to 
1,000 ohms. 

Another example may be found in measuring the 
resistance of an incandescent lamp hot and cold. 
If the A and B arms represent the ratio of 10 to 
1,000, and the C arm reads 4.5 ohms, what is the 
resistance of a lamp in the D arm? The lamp 
would have a resistance of 450 ohms cold but its 
resistance hot would be much less because when 
at incandescence it takes half an ampere and the 
resistance would be therefore 110^- = 220 ohms. 



94 ELECTRIC-WIRING, DIAGRAMS 

Almost any resistance high or low can be measured 
by the Wheatstone Bridge provided the galvanom- 
eter is delicate enough. The range of application 
reaches from .001 of an ohm to one million ohms 
with great accuracy, or a ratio of about i to one 
billion. 

Measuring Insulation Resistance. The measure- 
ment of insulation resistance is one of the most im- 
portant features of electric wiring because of the 
requirements of the Board of Fire Underwriters, 
who represent the insurance companies, and the re- 
quirements, self-imposed, by the contractor's con- 
science. 

Strange as it may seem to the uninitiated even 
the rubber or gutta percha covering of wires pos- 
sess a certain degree of conductivity. Where wire 
is used in large quantities this conductivity makes 
itself felt to such an extent that the resistance be- 
tween the copper wire and its covering is greatly 
reduced in proportion to the amount of wire used 
and the quality of the insulation employed. It is 
through this fact that the question of insulation 
resistance has arisen and requirements have been 
imposed limiting the amount of current and the 
insulation resistance in strict proportion to each 
other. In order to clearly convey an adequate idea 
of the meaning of insulation resistance as com- 
pared with metallic resistance a few illustrations 
will be necessary. 

Suppose 1,000 feet of No. 10 B. & S. wire are 
considered with a rubber covering of the regular 



AND SWITCHBOARDS 95 

character employed for insulated wire; the metallic 
resistance is only i ohm, but the insulation resist- 
ance may be anywhere from 100,000 to 1,000,000 
ohms. Supposing the insulation resistance is taken 
at 100,000 .ohms, then the question arises, what is 
the insulation resistance per foot, per yard and per 
hundred feet? This question can best be answered 
by means of an illustration (Fig. 24) conveying 
the correct idea. 



1000 FT. INSULATED WIRE 



INSULATION RESISTANCE 100,000 OHMS PER 1000 FT. 



500 FT. ..INSULATED WIRE 



INSULATION RESISTANCE 200,000 OHMS 500 FT. 



A I 250 FT. O 

[) INSULATED WIRE 4 " 

INSUTA'TION RESISTANCE 400,000 OHMS 



INSUCATION RESISTANCE 800.000 OHMS 125 FT. 

FIG. 24. Insulation Resistance of Various Lengths of Wire. 

The insulation resistance as shown by the illus- 
tration follows just the reverse rule of the metallic 
resistance. The insulation resistance increases the 
shorter the wire. If the data suggested by the 
above sketches is tabulated the following figures 
occur : 



9 6 



ELECTRIC-WIRING, DIAGRAMS 



Length of wire. 
Feet. 


Resistance of insulation. 
Ohms. 


1,000 


IOO,OOO 


500 


2OO,OOO 


250 


400,000 


I2 5 


8oo,OOO 


IOO 


1,000,000 


50 


2,OOO,OOO 


10 


IO,OOO,OOO 


I 


IOO,OOO,OOO 



The lesson taught by the above results is this, 
that the insulation resistance of each foot of wire 
must be very high in order to give a high general 
insulation resistance. The resistance of the wire 
may reach the same figure as the insulation resist- 
ance if enough of it be used as shown by the follow- 
ing figures : 



No. loB.&S. 
Feet. 


Resistance. 
Ohms. 


Insulation resistance. 
Ohms. 


1,000 


I 


IOO,OOO 


2,000 


2 


50,000 


10,000 


10 


IO,OOO 


100,000 


IOO 


1,000 


300,000 


3 00 


333 


i ,000,000 


1,000 


IOO 



The insulation resistance falls below the metallic 
resistance according to the above figures when the 



AND SWITCHBOARDS 97 

length of wire becomes greater than 300,000 feet 
of wire. This amount of wire seems enormous, but 
when the amount of wire installed in a World's 
Fair is considered and the wire installed in a 20- 
story skyscraper in New York City the drop in in- 
sulation resistance is a foregone conclusion. The 
question of insulation resistance is not merely that 
of the wires installed in a building, but also relates 
to power lines. The necessity for the use of relays 
in telegraphic service is largely due to the fact that 
the current leaks away in transit from one station 
to the other. As an example of this, supposing a 
telegraphic line 1,000 miles in length is considered. 
W r herever it is supported there is a glass insulator 
of at least 5,000,000 ohms (5 megohms) resistance. 
Every 200 feet (Fig. 25) another pole is erected, 



I ! 1 1 



}STATION[ LEAKAGE STATION] 

FIG. 25. Conditions Existing in a Long Distance Line. 

making about 25 insulators to the mile. Over a 
distance of 1,000 miles 25,000 insulators are neces- 
sary. This means an insulation resistance of 5,000,- 
ooo -7- 25,000 = 200 ohms over the line from end to 
end. This is under the best of conditions, when 
for instance the air is dry and the insulators clean, 
but in wet or stormy weather the conditions are 
different. The insulation resistance of not only 



9 8 ELECTRIC-WIRING, DIAGRAMS 

telegraph poles and lines but power lines as well 
drops considerably and a heavy leakage is apt to 
result. In the case of telegraph lines copper wires 
and high grade insulators may prove of some avail, 
but where serious leakage occurs with high tension 
power circuits a grave risk is incurred, beside 
which the mere question of the cost of power 
wasted loses its significance. 

Measurement of Insulation Resistance. To meas- 
ure a resistance of millions of ohms or megohms 
calls for a delicate and high resistance galvan- 
ometer and a box of high resistance coils (Fig. 
26). As shown in the sketches, the first process 



BOX OF COft-8 



GALVANOMETER 




FIG. 26. Connections for First Reading. 

is to connect the coils and galvanometer in series. 
Supposing the coils are unplugged and represent 
200,000 ohms and the galvanometer gives a reading 
of 20 divisions. The next step is to substitute the 
insulation resistance for the box of coils. The coil 
of wire is taped at one end and then immersed in 
a boiler of water or any other convenient metal 
receptacle (Fig. 27). The free end is connected in 
circuit and the metal vessel likewise connected as 
shown. The second reading may now be taken, 



AND SWITCHBOARDS 99 

it will be very low in all probability. If it is I 
division, then the resistance must be 20 X 200,000 
ohms = 4,000,000. 




GALVANOMETER) 

METAL RECEPTACLE 
HOLDING INS. WIRE 



FIG. 27. Connections for Second Reading. 

The current which has actuated the galvanometer 
has found its way through the insulation resist- 
ance of the wire and therefore the galvanometer 
indicates the respective quantities of current which 
flow when 200,000 ohms is in circuit in one case 
and the unknown insulation resistance in the other 
case. Interesting examples can be given in connec- 
tion with the wiring of buildings as follows : 

Example. What is the insulation resistance of 
a building using 20,000 feet of wire, the insulation 
resistance per foot being 10 megohms? The an- 
swer is readily obtained by dividing 20,000 feet 
into 10,000,000 ohms giving the result 10,000,000 
-f- 20,000 = 500 ohms. In other words, the follow- 
ing fact appears : That as the wire increases in 
length its metallic resistance increases but its in- 
sulation resistance decreases. 

Kinds of Insulation. The insulating material in 
vogue for the covering of copper wires may be 
roughly divided into four general classes. First, 



ioo ELECTRIC-WIRING, DIAGRAMS 

rubber; second, gutta-percha; third, composition, 
and fourth, cotton covering. The last, namely cot- 
ton, is in use for magnet and armature wire ; the 
first is generally employed for electric light wire 
which is usually advertised as rubber covered wire. 
Cotton covering saturated with paraffin is used in 
enormous quantities for bell and annunciator work, 
but a great deal of wire covered with composi- 
tion is also employed for this purpose. Atlantic or 
submarine cables are generally protected by gutta- 
percha coverings from the action of water but, in 
the course of time, changes in the character of the 
insulation take place and the rubber, gutta-percha, 
and particularly the composition coverings break 
down and the insulation resistance rapidly dimin- 
ishes. The deterioration is not of serious conse- 
quence if the wires are well protected in mould- 
ing or conduit, but in old-fashioned buildings, 
wired ten or more years ago, the risk of fire due 
to the general deterioration not only of the insula- 
tion but the switches, sockets, etc., is very great. 
The requirements of the Board of Fire Under- 
writers can be had on application, and a review 
of the conditions imposed will show the necessity 
for the selection of the best switches, sockets, 
wire and conduit in the equipment of a building 
for electric lighting. The systematic tests for in- 
sulation resistance which should be carried on will 
be a good indication of the value of the materials 
employed. If the lines are free from grounds and 
similar defects and the insulation resistance keeps 



AND SWITCHBOARDS 101 

falling it is a sign of the defective nature of the 
insulating covering of the wires. 

The Three-wire System. The two-wire system 
has been developed into a method of wiring, 
through which a great saving in copper is made. 
The employment of this method, under the title 
of the " three-wire system," by the present light- 
ing company in New York City, and its installa- 
tion as the wiring of thousands of private and pub- 
lic buildings establishes it as an economical and 
practical means of distributing current for electric 
lighting. 

The idea involved is that of making a more effi- 
cient use of the copper than would be possible in 
the method of employing only two wires for elec- 
tric lighting, as previously described. To illustrate 
theoretically and practically the advantages of the 
three-wire system reference must be made to the 
general principle underlying power transmission 
and its relation to the pressure in volts at which 
it is transmitted. The principle is stated as fol- 
lows : 

Principle. The weight of copper required for 
the transmission of a given amount of power is 
inversely proportional to the square of the pressure. 
By this is meant, that if 100 hp. is transmitted at 
loo volts pressure, and a certain weight, say 2,000 
pounds of copper, is required, then at twice the 
pressure or 200 volts only one-quarter or 500 
pounds of copper would be necessary. The fol- 
lowing table is instructive in showing how ad- 



102 ELECTRIC-WIRING, DIAGRAMS 



vantageous it is to use high pressures for the 
transmission of power in comparison with low 
pressures as far as the saving of copper is con- 
cerned. Taking the case of 100 kilowatts to be 
transmitted at 100 volts over a thousand foot run 
the following data appears : 













Volts. 


Circular 
mils. 


Kilo- 
watts. 


Length 
of wire. 
Feet. 


Weight 
of wire. 
Pounds. 


Drop. 

Volts. 


100 


440,000 


IOO 


2,OOO 


2,666 


5 


200 


110,000 


IOO 


2,OOO 


667 


10 


4OO 


27,500 


IOO 


2,OOO 


167 


20 


800 


6,875 


IOO 


2,OOO 


42 


40 


1,000 


4,400 


IOO 


2,000 


27 


50 


2,000 


1,100 


IOO 


2,000 


7 


IOO 



The remarkable reduction in the size of wire re- 
quired for the transmission of 100 hp. at 100 volts 
and at 2,000 volts, namely, 440,000 circular mils 
and i, 100 circular mils, is an object lesson in 
finance to builders of power transmission lines. 
The requirements for insulation naturally increase, 
but the cost of erecting the wire becomes much 
less on account of its lightness. A heavy line re- 
quires strong supports and great expense is in- 
volved if storms affect the stability of the line 
while in service. This is largely obviated where 
a light wire is run, that is to say, where a high 
pressure is employed. 



AND SWITCHBOARDS 103 

The three-wire system installed by the Edison, 
Company in the streets of New York consists of a 
network of copper embracing all of the downtown 
or business territory and following up the main 
thoroughfare, Broadway, with extensions to either 
side, thus covering an extensive area. If the three- 
wire system were not employed, that is, if the two- 
wire system were in its place at present, nearly 
three times as much copper would be in use to 
transmit the same amount of power. If, for in- 
stance, the above company has $1,000,000 worth 
of copper underground with the three-wire system, 
with the two-wire system there would be almost 
$3,000,000 worth installed. The principle, there- 
fore, has immense economical and practical advan- 
tages over the two-wire and in the following ex- 
planation the facts relative to this saving will be 
made clear: 

Suppose 100 lamps are to be lit on a loo-foot run 
at no volts pressure, then the size of wire accord- 



100 FT. 

[ = .117 OR 13750 C. M.=NO. 9 B. AND S. 





FIG. 28. 220 Volt Two-wire System Feeding 100 Lamps in Groups of 
Two in Series with 2 Per Cent. Drop. 

ing to the rule at a 2 per cent, drop would be 5,500 
circular mils or a No. 13 wire B. & S. gauge. If 
the voltage is doubled then 220 volts would call 
for every two lamps to be in series (Fig. 28), 



io 4 ELECTRIC-WIRING, DIAGRAMS 

,which would mean 50 sets of lamps of two in 
series, requiring only one-half the current of the 
other circuit of lamps. The first circuit called for 
50 amperes for 100-1 10 volt lamps on a two-wire 
circuit or 55,000 circular mils. The second circuit 
with every 2 lamps in series and 220 volts press- 
ure, calls for only 25 amperes. The drop in the 
second circuit is 2 per cent, or 4.4 volts while it is 
only 2.2 volts in the first circuit. In the second 
circuit, therefore, with 220 volts pressure, not only 
is one-half of the current required, which reduces 
the circular mils one-half but twice as many volts 
can be lost, which reduces the circular mils again 
to one-half. In other words, if a 220 volt pressure 
is used with the lamps arranged in groups of two 
in series, as shown, only one-quarter of the circular 
mils and therefore the weight of copper need be 
employed. 

But in the sketch shown, the number of lamps 
can be divided by 2 ; if one should burn out, the 
other connected to it would also go out, and this 
would make the system impracticable. Another 
reason why the system previously mentioned would 
be useless is where the number of lamps are un- 
equal, that is, not divisible by two. The use of 
the neutral wire shown in the sketch (Fig. 32) 
entitled " The three-wire system balanced," does 
away with both of these difficulties. In the sketch 
(Fig. 29) the three-wire system is shown un- 
balanced and the use to which the neutral wire 
is put in such a case. Its function is merely to 



AND SWITCHBOARDS 



105 



take up and transmit the current of the difference 
between the two sides of the circuit. If the neutral 

A B 




FIG. 29. The Three-wire System Unbalanced, Showing the Use of 
Neutral Wire with Respect to Three Lamps. 

wire were not employed, the amount of copper used 
at 220 volts, with groups of two lamps in series, 
would be only one-quarter, but with the neutral 
wire, for purposes of illustration, the same size as 
the two others, the amount of copper used becomes 
4 + -J + i t f what would be required to light 

100 FT. 
(Z-=.2345 OR 55000 C.M. = NO. 3 B. AND 8. ' 15 - 



100 LAMPS 
110 VOLTS 



, 



FIG. 30. Two-wire System. Size of Copper Wire. Lighting 100 
16 Candle Power Lamps, 2 Per Cent. Drop. 



100 FT. 
(Z=.117 OR 13750 C.M. =- No. 9 B. AND S. 



110 VOLT 
50 LAMPS 



110 VOLT 
LAMPS 






I, 



FlG. 31. Three- wire System. Size of Copper Wire. Transmitting 
the Same Power, 2 Per Cent. Drop. 

the same number of lamps at no volts by the two- 
wire system. The exact difference in the size of 
copper is shown by the sketches (Figs. 30 and 31) 



io6 ELECTRIC-WIRING, DIAGRAMS 

both as regards diameter in inches and circular mils 
in cross section. 

A simple calculation for obtaining the size of wire 
with a three-wire system with the same percentage 
of drop as a two-wire system is to employ the 
old formula with 4 in the denominator as follows : 
Circular mils = amperes X length of wire in feet 
X II -T- volts drop in line X 4, or, symbolically, 

ii X feet X C 
4 XE ' 

As regards the neutral wire in the laying out of a 
street system, such as is employed in New York, 
it is not as thick as the two outer wires but con- 
siderably less. The reason for this may be found 
in the fact that the lighting company will not 
turn current on the premises unless the lights are 
well balanced, therefore the amount of current 
carried by the middle wire is very small and its 
cross section in consequence is much less than 
the two outer wires. If the balance is fairly even 
throughout the district supplied with current, the 
generators connected to the circuit (Fig. 32) will 
carry equal loads; should a great difference of bal- 
ance exist, however, the load would become very 
heavy on one machine to the exclusion of the other 
and its injury would result. If the balance is on 
the average fairly good, the saving of copper 
through the neutral wire being small is greater, 
and instead of .375 of the copper being used, less 
will be required as compared with a two-wire sys- 



AND SWITCHBOARDS 



107 



tern. The same general ideas are carried out in 
the equipment of a building for a three-wire system 
as for a two-wire, with the addition that particular 



POSITIVE LEG 





NEUTRAL LEG 


1 




I 






1 1 


1 1 


220 VOLTS! 

NEGATIVE LEG j ] 














_ 



h-H 




U3 VOLT DYNAMOS 

FIG. 32. The Three-wire System Balanced. 

care is taken to keep the circuits balanced. In the 
following illustration (Fig. 33) is shown the gen- 
eral scheme of a three-wire system, lamps equally 
balanced, and special motor lines of 220 volts 
apiece. The idea can be still further carried out 
for a more extensive and more complicated circuit. 
The neutral wire in a perfectly balanced system is 
hardly necessary except in such cases as a few 
lights more are kept burning on one side of the 
circuit than on the other. 

Combination of Two and Three-wire Circuits. 
In many instances where private plants are in- 
stalled, the danger of a break-down has led the 
proprietor to make provision for such an emer- 
gency by having the wiring done so as to take cur- 
rent from the street if necessary, without risking 



io8 ELECTRIC-WIRING, DIAGRAMS 

the lamps in ordinary use. This is accomplished 
by equipping the building with the three-wire sys- 
tem but making the neutral wire of twice the cross 



220 VOLT MOTOR 



220 VOLT MOTOR LINE 




FIG. 33. Three-wire System with Two Centers of Distribution 



AND SWITCHBOARDS 



109 



section of the two outer wires. By this means both 
a no- volt two- wire system and a 220- volt three- 
wire system are combined (Fig. 34) and the equip- 




FIG. 34. Combination of Two and Three-ware System for Protection 
Against Break-down of Private no- Volt Two- wire System. 

ment will work admirably on either, if the circuits 
are balanced. There is a distinct saving of copper 
by this method of wiring over the two-wire system, 
because according to the figures previously given, 
three wires, if of equal size, represent .375 of the 
copper which would be required in a two-wire sys- 
tem of equal capacity. Each wire is therefore one- 
eighth, and if the middle wire is twice the circular 
mils of the other two the total will be J + 4 + 4 = 
^, or .50. In other words, a building wired accord- 



no ELECTRIC-WIRING, DIAGRAMS 

ing to the above requirements is still using only 
one-half the copper otherwise required by a two- 
wire system. 

In handling heavy wires it is frequently neces- 
sary to be able to calculate the weight of the wire, 
as for instance in considering the mains and feeders 
of a large installation. The formula for doing this 
is as follows : 

Pounds per foot of copper = circular mils 

C M 
-v- 62.5 X 5,280 = 



62.5 X 5,280 

By leaving out the 5,280 the weight of copper per 
mile is obtained and the formula becomes: Weight 
in pounds per mile = C. M. -f- 6.25. In power lines 
for motors or lighting, this calculation is very valu- 
able, as in the preparation of estimates many 
means are adopted to keep the weight of copper 
down. 

Example. As an example of the above, suppose 
200 hp. is to be transmitted one mile at 500 volts 
and 5 per cent, drop, what is the size and weight 
of the wire? 

r . i ., 300X10,560X11 

I he circular mils = - = 1,393,920. 

The weight per mile = ^ = 22,303 pounds for a 
single wire or a total of 44,606 pounds per mile. 

The weight per foot =? - I>3 93>9 2 = 3.44 pounds. 



AND SWITCHBOARDS in 

The above figures are indicative of the necessity 
of estimating drop as high as is consistent with 
good engineering or the weight of the copper be- 
comes excessive. 

The law promulgated by Lord Kelvin years ago 
reads as follows: The cost of copper must be such 
that the interest on the investment shall not exceed 
the cost of wasted power in the line. The meaning 
of this is that with $100,000 spent for copper in a 
transmission system only $6,000 worth of power 
should be wasted, because this represents the in- 
terest on the investment. 



ii2 ELECTRIC-WIRING, DIAGRAMS 



CHAPTER V 

TYPES OF MOTORS. CONNECTIONS OF MOTORS. MEANING 
AND REASON FOR BACK ELECTROMOTIVE FORCE. 
USE OF A STARTING BOX. METHOD OF CONNECTING 
UP A SHUNT WOUND MOTOR. HORSE POWERS OF 
MOTORS AND EFFICIENCIES. EFFICIENCY OF MOTORS 
AND SIZE OF WIRES. ADVANTAGE OF HIGH PRESS- 
URES. THE ALTERNATING CURRENT FOR LIGHTING. 
MEANING OF FREQUENCY OR CYCLES. 

THE subject of wiring is closely related to power 
transmission both as regards the wiring and the 
motors operated from distant sources of power. 
It is within the scope of wiring treated as a science 
as well as an art to consider the motor and briefly 
outline its principles of operation and construction. 
Motors are generally divided up as far as continu- 
ous current circuits are concerned into three great 
classes as follows : 

The Series Wound. 

The Shunt Wound. 

The Differentially Wound. 

This classification relates to the winding of the 
magnets or fields, as they are commonly called. 
The manner in which the field is affected by the 
current flowing through its coils is indicated in the 
above tabulation and sketches (Figs. 35, 36 and 37). 



AND SWITCHBOARDS 



FIG. 35. Connections of a Series Wound Motor. 




FIG. 36. Connections of a Shunt Wound Motor. 




FIG. 37. Connections of a Differentially Wound Motor. 

The Principle of the Motor. The motor and 
dynamo are reversible machines, the dynamo trans- 
forming mechanical energy into electricity, the 



n 4 ELECTRIC-WIRING, DIAGRAMS 

motor transforming electrical energy into mechan- 
ical force. Any well made dynamo will operate 
successfully as a motor, in fact there is in many 
cases only a difference in name between the two 
machines. A dynamo is a machine in which the 
movement of conductors through the magnetic 
field (Fig. 38) means the development of electro- 




FIG. 38. Conductor Cutting Lines of Force. 

motive force. As these conductors produce more 
current the source of mechanical energy is called 
upon to deliver more power until a balance is estab- 
lished. In a motor the same conditions exist in a 
reverse manner ; the demand for more current takes 
place automatically until sufficient enters to do the 
work required by the outside load, whereas in the 
dynamo the extra lamps or motors turned on rep- 
resent the demand for more current, and hence 
more mechanical energy. In the motor the extra 
current automatically and instantaneously augments 
as extra strain is put upon the motor. In the motor 
as well as the dynamo conductors rotate in a mag- 
netic field. The consequence is that electromotive 
force is developed which in the case of the dynamo 



AND SWITCHBOARDS 115 

is utilized for lighting, etc., "but in the case of the 
motor this electromotive force is opposed to the 
electromotive force sending a current through the 
armature and is therefore called the " back EMF." 
The armature of a motor is simply an electro-mag- 
net which experiences a series of attractive pulls, 
when current enters its winding through the action 
of the commutator and the position of the brushes. 

The commutator and brushes constitute an auto- 
matic switch which sends the current into certain 
coils in certain positions on the armature. These 
coils magnetize the core of soft iron and a powerful 
tractive effort develops between the armature and 
the magnetic poles which embrace it. Summing 
the phenomena up, therefore, the action in a motor 
is simply the attraction between opposite magnetic 
poles which results in continuous rotation. As far 
as the mechanical results are concerned this is 
about all that need be said in a brief review of the 
situation, but the reactions occurring within a motor 
call for recognition in the scheme of wiring and 
reference must therefore be made to them. 

Effect of Back emf. upon Wiring. The armature 
of a motor cannot instantaneously spin around at 
a high rate of speed, when current is turned on, 
therefore it cannot generate a back EMF. in time to 
stem the flood of current which will pour through 
it. A heavy flow will take place because the re- 
sistance of the armature is too low to prevent it. 
It is necessary to interpose between the armature 
and the line a resistance (Fig. 39) sufficiently great 



u6 ELECTRIC-WIRING, DIAGRAMS 

to check any unusual flow of current. In the shunt 
and differentially wound motors this is imperative ; 
in the series wound motor it is only necessary under 



RESISTANCE. 



FIG. 39. Principle of the Connections of a Shunt Motor. 

certain circumstances. The current is restrained 
until the armature has gained sufficient speed to 
generate the required back EMF. to establish a bal- 
ance between the power entering the motor and 
the effort called for by the load. The resistance 
is then cut out and the motor regulates its own 
influx and efflux of current by the back EMF. and 
this in its place is regulated by the load. In the 
following sketch (Fig. 40) a shunt motor is shown 
with the starting box interposed when the armature 
begins to rotate. The boxes are so constructed 
that the final movement of the handle cuts out all 
resistance and connects the motor to the mains. 

Points About Motors. In the wiring of a shunt 
motor the fields must be on first and the pole pieces 
must be tested to discover this fact. Next, the cur- 
rent must pass into the motor through the resist- 
ance box and the armature will start slowly. The 
final throw of the handle of the starting box must 



AND SWITCHBOARDS 



117 



not cause any unusual development of speed. A 
series motor must never be started without a load 
on. If this rule is not observed the motor will ro- 




FIG. 40. Practical Connections of a Shunt Motor. 

tate at an enormous rate of speed, each accession 
of speed developing a velocity which will only cease 
by the opening of the switch or the destruction of 
the motor. 

A differentially or compound wound motor repre- 
sents a combination of the two windings. The 
principle involved is this : that by weakening the 
field of a shunt motor the speed of the armature 
increases. In consequence, the current in the series 
coil of the motor tends to reduce the strength of 
field and increase its speed "when the load tends to 
diminish it. 

Efficiency of Motors. The efficiency of the motor 



n8 ELECTRIC-WIRING, DIAGRAMS 

is twofold, the electrical efficiency and the commer- 
cial efficiency. The electrical efficiency is the ratio 
between the back EMF. and the impressed or ex- 
ternal EMF. The commercial efficiency is the ratio 
between the power given out by the motor and the 
power it absorbs. Unless a motor has a high elec- 
trical efficiency it cannot have a high commercial 
efficiency. The back EMF. and therefore the elec- 
trical efficiency can be calculated in the following 
manner : Multiply the resistance of the armature by 
the current and subtract the product from the im- 
pressed EMF. to get the back EMF. For instance, 
suppose a motor has an armature resistance of .01 
of an ohm and takes 50 amperes at no volts, what 
is the back EMF. ? According to the above principle 
50 X .01 = .50 and subtracting .5 from no gives 
109.5 back EMF. The electrical efficiency equals 
109.5 -T- no or 99.5 per cent. If the power devel- 
oped in this case equals 5 hp. then the commercial 
efficiency equals 5 X 74^ -r- 5,500 = 3,730 -r- 5,500 = 
67.5 per cent. 

In motor wiring calculations the commercial effi- 
ciency is of the greatest consequence if given in 
connection with the EMF. of the motor. The cir- 
cular mils required for a motor line can be calcu- 
lated if the horse power of the motor, its efficiency, 
the voltage, the length of the line and the drop are 
given. The formula for calculating the circular 
mils is as follows: 

_ HP. of motor X 746 X length of wire X n 
volts of lines X drop X efficiency in %. 



AND SWITCHBOARDS 



119 



Taking a practical case, what are the circular mils 
of a motor line with the following data: 

HP. of motor = 10. 

Length of run = 200 feet. 

Volts of line = 220. 

Drop of line = 10 volts. 

Efficiency = 80 per cent. 

C. M. = 10 X 746 X 400 X ii -r- 220 X 10 X .80 
= 18,650 or a No. 7 B. & S. To check the results 
find the resistance of 400 feet of No. 7 wire and 
multiply by the current, which in this case is ap- 
proximately 50 amperes. 

Resistance 400 feet No. 7 = .2 ohm. .2 X 50 = 10 
volts drop as indicated above. 

The efficiencies of motors vary very much, but 
the average efficiency of the general run of direct 
current motors can be summed up in the following 
figures : 



Horse power. 


Efficiency. 


I 


70 per cent. 


2 


75 per cent. 


3 


80 per cent. 


4 


82 per cent. 


5 


85 per cent. 


6 


87 per cent. 


7 


88 per cent. 


8 


89 per cent. 


9 


90 per cent. 


10 


91 per cent. 



120 ELECTRIC-WIRING, DIAGRAMS 

A comparative table showing the relationship 
between the efficiency of a motor and the size of 
wire required will be instructive in showing how 
a low efficiency and high efficiency motor affect 
the contractor's expense in wiring: 



Efficiency of motor. 


Circular mils. 


50 per cent. 


29,840 


55 per cent. 


27,127 


60 per cent. 


24,866 


65 per cent. 


22,938 


70 per cent. 


21,314 


75 per cent. 


iQ 8 93 


80 per cent. 


18,650 


85 per cent. 


i7553 


90 per cent. 


J 6,577 



The above table is built from the problem just 
given with a 10 hp. motor and 80 per cent, effi- 
ciency, only the efficiencies are varied to show the 
change in the size of wire required. This problem 
is of the utmost importance, particularly in power 
transmission, where the weight of copper when 
heavy horse powers are transmitted becomes enor- 
mous unless limited by high pressures and efficien- 
cies. The weight of copper can be likewise devel- 
oped with respect to the efficiency as shown in the 
following table, in which one mile of wire is con- 
sidered, a 10 hp. motor and 500 volts pressure : 



AND SWITCHBOARDS 121 



Efficiency. 


Weight in pounds 


per mile 


50 


1,109 




60 


924 




70 


792 




80 


693 




90 


616 





The tendency on all sides is to adopt high press- 
ure systems which represent a combination of direct 
and alternating current machinery. 

The Alternating Current. In .the lighting of in- 
candescent lamps alternating as well as direct cur- 
rent is employed. The alternating current differs 
from the direct current in so far as it consists of 
a series of systematic impulses or waves which 
rush back and forth in the circuit a certain number 
of times a second. The dynamo generating an 
alternating current becomes an alternator simply 
because it has no commutator, the armature wind- 
ing ending in two rings instead of being connected 
to copper strips insulated from each other. The 
direct current dynamo also generates an alternating 
current, but this current is modified in the sense 
that its impulses are all sent along in the same 
direction by means of the commutator and brushes. 
The original name for the commutator was recti- 
fier, because it rectified the impulses. There are 
various characteristics to alternating currents which 
must be known in the handling of them for com- 
mercial purposes. 



i22 ELECTRIC-WIRING, DIAGRAMS 

The frequency or number of periods per second 
is the term used to define the number of complete 
reversals (Fig. 41) of current per second. Each 





FIG. 41. Rise, Fall and Reversal of Electromotive Force in an 
Alternator. 

complete reversal is due to the wire passing two 
poles a north and a south pole. While passing 




FIG. 42. Elements of an Alternator. 

before the north the current flows in one direction 
(Fig. 42), and when passing the other in the oppo- 



AND SWITCHBOARDS 123 

site direction. The frequency or number of periods 
per second can therefore be calculated in the fol- 
lowing manner: 

Frequency. The frequency = revolutions per 
second X one-half the number of poles. For in- 
stance, what is the frequency of an alternator with 
8 poles and a speed of 30 revolutions per second? 
Frequency = 30 X 4= 120 reversals. The utiliza- 
tion of an alternating instead of a direct current is 
due to many advantages in transmission possessed 
by an alternating current system over a direct. 
This first manifests itself in a great saving in 
copper and power, secondly in cost of construction 
of both dynamos and line. In connection with 
wiring the question which arises is this, " Is the 
line inductive or non-inductive?" In other words, 
are coils in any way associated with the circuit so 
as to develop reactive electromotive forces or not. 
It is therefore necessary in preparing the plans of 
an alternating current lighting and power system 
to be sure that the circuits are free from disturbing 
inductive influences. 



i2 4 ELECTRIC-WIRING, DIAGRAMS 



CHAPTER VI 

REASONS FOR EMPLOYING CONDUIT. THE USE OF CLEATS. 
THE USE OF MOULDING. IRON ARMORED CONDUIT. 
ENAMELED IRON CONDUIT. BRASS ARMORED CONDUIT. 
ASPHALTIC PAPER TUBE OR PLAIN CONDUIT. FLEX- 
IBLE WOVEN CONDUIT. FLEXIBLE METALLIC CONDUIT. 
THE USE OF BENDS, ELBOWS, OUTLET AND JUNCTION 
BOXES. DIRECTIONS FOR INSTALLING CONDUIT. CON- 
DUIT JOBS AND THEIR ACCESSORIES. SCHEDULE FOR 
WIRING SYSTEMS. 

Reasons for Employing Conduit. Twenty years 
ago electric lighting had not impressed business 
men sufficiently with its advantages and practical 
value to represent anything more than an experi- 
ment. The dynamos were in a comparatively crude 
condition and their regulation imperfect. A very 
small portion of the city's area was strung with 
electric wires, and in consequence thousands of 
poles and an aerial network greeted the eye, com- 
posed of electric light wires, high tension and low, 
telegraph wires and telephone wires. These wires 
crossed' each other and frequently high tension 
currents poured into low tension lines, and the 
wiremen engaged in repairing circuits were often 
the subjects of tragic scenes. Deaths became so 
recurrent through confusion and accident that the 



AND SWITCHBOARDS 125 

municipality decided to pass laws to avoid future 
trouble and demand that all wires be put under- 
ground. One of the first to observe this law long 
before it was passed, due largely to the necessity 
of the occasion, was the Edison Lighting Com- 
pany. It placed its wires underground in iron pipes 
and employed junction boxes and outlet boxes, in 
what was perhaps the first underground conduit 
system in New York City and in all probability in 
the United States. The repeated fires attributed 
in many cases to electric light wires brought the 
attention of the Fire Underwriters to residences, 
business houses, and public buildings with the re- 
sult that much wiring already installed was con- 
demned and a new code of rules framed which in- 
cluded the use of what was then called " interior 
conduit " for house wiring. At first merely paper 
tubing soaked in asphalt was used, then the tubing 
was armored with brass, and finally further pro- 
tection was sought against mechanical injury by 
the use of iron pipe conduit, at present greatly in 
vogue. 

Conduit Wiring. The different kinds of wiring 
are included under the heads of 

i Knob or insulator wiring. 

2 Cleat work. 

3 Moulding work. 

4 Conduit work. 

For exposed work the first three methods (Figs. 
43, 44, 45 and 46) may be employed although the 
third, moulding work, is the most ornamental of 



126 ELECTRIC -WIRING, DIAGRAMS 



me. 



FIG. 43. Porcelain Cleats. 





) I 



FIG. 44. Knob Insulator. 



FIG. 45. Cleat Carrying Wires. 




FIG. 46. Moulding Carrying Wires. 



AND SWITCHBOARDS 127 

the three. The last, conduit work (Fig. 47), is 
done either exposed or concealed. If exposed, as 
is the case in the railway stations connected to the 




FIG. 47. Conduit Carrying Insulated Wire. 

electric elevated service of New York City, no 
architectural difficulties present themselves ; but 
where the work is concealed, questions arise of a 
more complicated nature. An old building or one 
recently constructed may be wired for electric 
lights and conduit installed. In this case the walls 
and ceilings must be grooved and the floors torn 
up, making an exceedingly expensive and trouble- 
some job for the contractor, attended with many 
risks. On the other hand the conduit may be in- 
stalled in a new building before the plasterers get 
to work. In this case the work can be done with 
comparative ease and facility and a corresponding 
cheapness in cost. In either case the plan of wir- 
ing must be carefully worked out on paper so that 
no delays are experienced on this score. Where 
conduit is used different diameters of pipe must be 
employed because of the varied diameters of the 
wires. There are many different kinds of conduit 
turned out by the principal manufacturers, but 
they may all be generally grouped under the head- 



128 ELECTRIC-WIRING, DIAGRAMS 

ings of Iron Armored Conduit, Brass Armored 
Conduit, Flexible Metallic Conduit, Flexible Non- 
metallic Conduit, Asphaltic paper, or composition, 
called Unarmored Conduit. 

The installation of a conduit system is practically 
equivalent to the equipment of a house with pipes, 
exposed or concealed as the case may be, through 
which wires are fished after the pipe work is com- 
pleted. The necessity for using conduit of the 
correct size need hardly be commented upon. The 
greatest difficulty will be experienced if the pipes 
catch or grip the wires when they are fished 
through, and it is imperative therefore to only use 
the correct diameters, leaving nothing to chance 
in this respect. It occasionally happens in tall 
buildings that when mains or feeders are pulled 
through a conduit having several bends enormous 
force is necessary. This may be due to a kink in 
the wire or the bends or elbows in the pipe. A wire 
may slip through a pipe easily, yet catch if an 
elbow or two present themselves. A liberal allow- 
ance in pipe diameter will obviate this and save 
time and necessarily labor and expense if consid- 
ered in advance in the wiring plans. 

The standard sizes of conduit are given with 
reference to the inside diameters of the different 
samples. The inside diameters of iron armored 
conduit as given by one of the foremost manufact- 
urers are as follows : 



AND SWITCHBOARDS 



129 



IRON ARMORED CONDUIT. 



Inside 
diameter. 


Outside 
diameter. 


. Inside Outside 
diameter. diameter. 


& 


.675 


I* 


I.QO 




.84 


iA 


2-375 


TV 


1.05 


2i 


2-875 


A 


I-3 1 


2f 


3-500 


ii 


1.66 







This conduit is made of standard weight iron 
pipe and the same rules are followed in installing 
it that relate to wiring in general. Whenever dif- 
ferent sizes of wire are to be connected a cutout 
must be installed and the circuits therefor radiate 
from or converge to panel boards. This is entirely 
in line with any other system of wiring whether 
knob, cleat or moulding. The iron armored con- 
duit consists of iron pipe lined inside with insulat- 
ing material, either a bushing or a composition in 
the form of a paint or enamel. 

Enameled iron conduit is the name especially 
applied to "iron pipe with an insulating enamel in-, 
side. As a general rule manufacturers guarantee 
that their product will bend without breaking or 
cracking the enamel. The inside and outside 
diameters are as follows: 



130 ELECTRIC-WIRING, DIAGRAMS 



ENAMELED IRON CONDUIT. 



Standard size pipe. 
Inches. 


Actual internal 
diameter. Inches. 


Actual outside 
diameter. Inches. 


1 


.62 


.84 


1 


.82 


1.05 


I 


1.04 


I-3I 


ii 


1.38 


1.66 


i* 


1.61 


1.90 


2 


2.06 


2 -37 


2* 


2.46 


2.87 


3 


3.06 


3-5o 



The brass armored conduit consists of a compo- 
sition of compressed paper saturated with an in- 
sulating solution and then protected on the outside 
with brass sheathing tightly embracing the inner 
thicker walled tube of conduit proper. The sizes 
of this material are as follows : 



BRASS ARMORED CONDUIT. 



Inside diameter. 



Inside diameter. 



T 5 -g- inch. 
| inch. 
J inch. 
| inch. 



} inch, 
i.o inch. 
1 1 inch, 
i inch. 



In choosing conduit for a job care must be made 
in the selection that the wire can be pulled through 



AND SWITCHBOARDS 131 

freely, otherwise great difficulty will be experienced 
when this point of the work is reached. 

The asphaltic paper tube runs into smaller sizes 
than the others. It is called plain conduit and rep- 
resents the first type of tubing employed years ago 
for the protection of wires as a substitute or equiva- 
lent for moulding. The sizes are as follows : 

ASPHALTIC PAPER TUBE OR PLAIN CONDUIT. 



Inside diameter. 


Inside diameter. 


J inch. 


i inch. 


-fa inch. 


ij inch. 


| inch. 


i inch. 


f inch. 


2 inch. 


} inch. 


2\ inch. 



Unarmored like the above is the tubing called 
the American Circular Loom Conduit. It consists 
of woven insulating tubing, flexible in character 
and of great convenience in bridging over other 
circuits. It is used to a great extent for switch- 
board work and is extensively used for general 
wiring. Where wires are exposed and turns are 
to be made it finds ready application. Before the 
insurance laws became so far reaching and iron 
pipe was required, the flexible conduit enjoyed un- 
disputed supremacy in the commercial field. The 
inside diameters are given in the following table: 



132 ELECTRIC-WIRING, DIAGRAMS 

FLEXIBLE WOVEN CONDUIT. 



Inside diameter. 


Inside diameter. 


J inch. 


J inch. 


| inch. 


i inch. 


J inch. 


ij inch. 


| inch. 





In conjunction with the woven conduit there is 
also the flexible metallic conduit which is exten- 




FIGS. 48 and 49. Method of Securing Flexible Metallic Conduit. 

sively employed in wiring (Figs. 48 and 49). The 
sizes as regards the inside diameters are as follows : 

FLEXIBLE METALLIC CONDUIT. 



Inside diameter. 


Inside diameter. 


T 6 ^- inch, 
f inch. 
J inch. 


J inch, 
i inch, 
ij inch. 



AND SWITCHBOARDS 133 

With all metallic conduits whether flexible or not 
there are employed junction and outlet boxes (Figs. 
50, 51, 52, 53 and 54). They are either round 




FIG. 50. Bend. 




FIG. 51. Coupling. 




Fio. 52. Elbow Clamp. 

lined or square lined and serve for the purposes in- 
dicated by the names ; either to allow wires to pass 



i 3 4 ELECTRIC-WIRING, DIAGRAMS 

out for lamps, chandeliers, etc., in which case out- 
let boxes are used, or to act as boxes in which junc- 
tions are made between circuits, hence the title. 




FIG. 53. Outlet Box. 




FIG. 54. Junction Box. 

A unique combination of both wire and conduit 
in one has been introduced to the wiring world 
under the name of flexible steel-armored conduc- 



AND SWITCHBOARDS 135 

tors. The purpose of this invention is primarily 
to develop a system by which wires can be installed 
where an ordinary conduit system would be a fail- 
ure. The ease with which wiring can be installed 
when the conductors are so protected represents 
a saving in labor that relieves the problem of what 
might otherwise be regarded as unusual expense. 
Then in such cases where wires could not be 
safely or securely installed the application of this 
system becomes an absolute necessity. To quote 
from the manufacturers' catalogue " the flexible 
steel armored conductors (Figs. 55 and 56) are of 




FIG. 55. Flexible Steel Armored Conductors. 

special value for use under conditions, which would 
make difficult, if not impossible, the installation 
of a conduit system. The steel armor affords ample 
protection against ordinary mechanical injury, and 



136 ELECTRIC-WIRING, DIAGRAMS 

conductors so armored can easily be drawn or 
fished into a building between partitions and under 
floors. In such cases no fastenings are required 




FIG. 56. Steel Armored Flexible Cord. 

except at the outlets. When so installed, these 
conductors may be removed, if desired, as easily as 
the wires could be drawn from a conduit. The 
lead-covered, steel-armored conductors are of spe- 
cial value in damp places, such as breweries, dye 
houses, stables, etc., and are specially recommended 
with twin conductors for marine and underground 
work." 

The conduit generally installed is held in place 
by means of fasteners or straps. 

The lengths of conduits are joined together by 
couplings. When the flexible conductors are twin 



AND SWITCHBOARDS 137 

or three conductors their special adaptability for 
marine service becomes pronounced. They are 
generally made of stranded wires, that is, many 
fine wires together to give flexibility to the con- 
ductor. The sizes are as follows: 



FLEXIBLE STEEL ARMORED (SIZES). 



Twin. 


Marine work. 


Single conductor. 


14 
12 


14 Twin. 
1 2 Twin. 


IO 
8 


IO 


ioT\vin. 


6 


8 
6 




4 

2 






I 



The couplings for ordinary conduit work run 
through a variety of sizes extending from J- up, 
depending on the character of the conduit, whether 
iron armored, brass armored or flexible, etc. In 
addition, elbows are employed where bends or 
turns are to be made. The various elements of a 
conduit system can be included under the following 
classification : 



138 ELECTRIC-WIRING, DIAGRAMS 



Character of conduit. 



Iron armored. 



Brass armored. 



Plain unarmored, 



Accessories. 



Iron elbows. 

Iron couplings. 

Plugs. 

Lock nuts. 

Tees. 

Caps. 

Malleable iron unions. 

Straps. 

Elbows. 

Couplings. 

Straps. 

Elbows. 

Couplings. 

Straps. 



The flexible metallic conduit system calls for 
about the same accessories as the iron armored, 
the only difference being the flexibility of one in 
contrast with the other, and therefore the absence 
of elbows. Whenever special devices are to be 
employed, the manufacturers are only too happy 
to give full information and, if necessary, to make 
such changes or improvements as are required. 
Each conduit system calls for a special set of tools 
and it is necessary to possess experience and skill 
to properly install a conduit system and handle the 
tools relating to it. The time allowed for installing 
a conduit system of the concealed type is neces- 



AND SWITCHBOARDS 139 

sarily limited by the fact that the plasterers follow 
the electrical workers. Such being the case little 
time is left to rectify mistakes ; should they be 
discovered after the plaster has been laid the con- 
tractor will be put to considerable expense. In 
many important cases the plans are either drawn 
up or at least vised by a competent consulting en- 
gineer to facilitate the completion of the work and 
rest the responsibility for it. 

There are many kinds of wiring which must be 
done to fulfill the requirements of the specifications. 
These specifications cover the character of wiring 
and the number of outlets as well as the purpose 
for which they will be used. 

The system of wiring to be employed is also 
specified and must be carefully planned out and 
observed in the subsequent work. 

WIRING SYSTEMS. 

Three-wire system, iron conduit, direct current. 

Two-wire system, iron conduit, direct current. 

Two-wire system, iron conduit, alternating cur- 
rent. 

Two and three-wire system, iron conduit, for 
direct and alternating current. 

The last system refers to a combination wiring 
plan, the wires protected in conduit, to be con- 
nected to either the three-wire system of the street 
service or a private two-wire plant in the building. 
A schedule can be prepared which will include the 



140 ELECTRIC-WIRING, DIAGRAMS 

general method of wiring, the system of conduit 
work, the exact voltage to be supplied and the 
character of the current whether direct or alter- 
nating. 



System. 


Schedule. 


Volts. 


Two-wire. 


No. of mains. 


no 




No. of feeders. 






No. of risers. 






No. of sub-mains. 






No. of branches. 





A more elaborate schedule can be worked out 
comprising all the details of a wiring proposition, 
but for general practical purposes the above is 
sufficient. 

According to an authority, from whose words 
the following definition and requirements are taken 
with reference to the purpose in view in using con- 
duits "The object of a tube or conduit is to facili- 
tate the insertion or extraction of the conductors, 
to protect them from mechanical injury, and as 
far as possible from moisture. Tubes or conduits 
are to be considered merely as race ways, and are 
not to be relied on for insulation between wire and 
wire, or between the wire and the ground." Con- 
duits themselves must meet with certain require- 
ments before they can be considered fit or safe to 
use. 



AND SWITCHBOARDS 141 

Although many types can be selected, the condi- 
tions for their installation and for governing their 
selection may be better understood with reference 
to the following limitations : 

GENERAL REQUIREMENTS FOR CONDUIT. 

I. The conduit between junction box and junc- 
tion box must be continuous. 

II. It must be continuous between junction box 
and fixtures. 

III. It must be composed of such material or 
be of such construction that neither the insulation 
of the conductor or the insulation within the tube 
itself will be ultimately affected or deteriorated. 

IV. The conduit must be of such material that 
it will resist the effects of heat ; it must not ignite 
or burn through the overheating of fusion of wires 
within it. 

V. It must be strong and hard enough to resist 
blows of hammers, the action of saws, or the points 
of nails or screws. It must, in fact, be able to resist 
mechanical injury due to these causes without col- 
lapse or fracture. 

VI. It must be capable of being installed as a 
complete pipe or conduit system without conduc- 
tors so that all heavy work on the building can be 
completed before the wires are pulled through their 
respective tubes. 

It might be added with reference to these facts 
that the risk of installing more than one wire in a 



142 ELECTRIC-WIRING, DIAGRAMS 

tube is so great as to be, except where particu- 
larly specified, forbidden by the Fire Underwriters. 
Where specially approved steel or iron conduit is 
installed, permission to use twin conductors or two 
conductors in the conduit is a matter of discretion 
on the part of the authorities. When iron or steel 
armored conduit meets with the approval of the 
Fire Underwriters it must be able to meet such 
requirements as are embodied in the following 
chapter. 



AND SWITCHBOARDS 143 



CHAPTER VII 

REQUIREMENTS FOR IRON AND STEEL ARMORED CONDUIT. 
LAYING OUT A CONDUIT SYSTEM. THE INSULATION OF 
CONDUCTORS. MECHANICAL WORK. INSULATING MA- 
TERIALS. CONCEALED AND EXPOSED WORK. INSULA- 
TION RESISTANCE. GROUNDED WIRES. SOLDERING 
SOLUTION. A DISTRIBUTION SHEET FOR LAYING OUT 
WIRING. 

Requirements for Iron and Steel Armored Con- 
duit. a. When the tube is grounded to one leg 
of the circuit and the wire to the other, the volatili- 
zation of all or part of the wire when it is " burnt 
out " must not injure the tube. 

b. The insulating protective coating inside the 
tube must not become soft at a lower temperature 
than 158 degrees F. (70 degrees C.). 

When water is boiled inside the tube it must not 
dissolve the constituents of the insulation but must 
remain in its original condition. 

c. The effect of immersion or soaking in water 
for a few days must not so affect the mechanical 
integrity of the insulating material that it becomes 
weak and therefore useless. 

d. The insulation resistance of the tube must 
remain high, if the length of tube is bent and filled 
with water and a test made at the end of three 



i44 ELECTRIC-WIRING, DIAGRAMS 

days. The insulation resistance under these cir- 
cumstances between the metallic pipe and its con- 
tents must not fall below I megohm. 

In order to continue the remarks to be made in 
general about conduit, its requirements and its in- 
stallation it may be further stated that all conduit 
ends projecting must be filled with an insulating 
compound to protect its contents from moisture 
and deterioration. This practice must be followed 
out at the junction boxes as well, and particular 
attention must be paid to all joints which accord- 
ing to requirement must be made moisture-proof 
and air-tight. 

As regards the finishing of the ends of project- 
ing conduits, these must extend at least I inch be- 
yond the mortar or plaster because of the possi- 
bility of moisture and foreign matter otherwise 
entering the tube. If necessary, this projection may 
be subsequently cut down, but it must project at 
least J inch beyond the wall surface when said 
surface is finished. These requirements are en- 
tirely in line with the dictates of practice and 
reason and mean the avoidance of trouble, both 
with regard to the choice of conduit and its instal- 
lation. 

Laying Out a Conduit System. In laying out 
the plans of a conduit system certain responsibili- 
ties rest with the architect as well as the consult- 
ing engineer or contractor. The demands made 
upon the contractor and consulting engineer relate 
to the mapping out of the work and its subsequent 



AND SWITCHBOARDS 145 

installation. That of the architect relates to the 
provisions made in the construction for the recep- 
tion of the conduits in a convenient and practical 
manner. The architect's duties consist, therefore, 
in making provision when preparing the plans of 
the building, for such ducts, pockets and channels 
as may be required for the conduits and the electric 
light and power lines they carry. 

Insulation of Conductors. The great danger of 
grounds and short-circuits in buildings may be re- 
duced to a minimum if the general principle is 
followed out when installing wires of regarding 
their installation, however good, as non-existent. 
If wires are installed in buildings, whether in con- 
duit, moulding or on insulators as if they possessed 
no insulation, but were bare, then the precautions 
taken would be so far reaching that the risk of 
faults from grounds or poor insulation is negligible. 

Mechanical Work. Too much stress cannot be 
laid upon the necessity for as perfect mechanical 
work as can be done. The details of soldering 
and connecting wires, the taping of wires and the 
proper method of securing the conduit all of 
these belong to the field of purely practical work 
calling for experience and skill on the part of the 
employes. Efficiency can only be secured if every 
portion of the conduit and conductor undergoes a 
careful inspection during the development of the 
work and during its completion. The best point 
from which to start, whether the wiring or conduit 
is being installed, is the center of distribution. 



146 ELECTRIC-WIRING, DIAGRAMS 

After one or many have been selected, by a care- 
ful examination of the conditions, then it is neces- 
sary to select the correct points at which the 
switches and cutouts controlling the different cir- 
cuits are to be placed. In order to render such 
positions accessible for ready handling in case of 
short-circuits, grounds, breaks or other faults, panel 
boards are generally employed. These boards are 
miniature switchboards at which all the circuits of 
a part of a floor, or of one or two floors, converge. 
They are the sub-centers of distribution of a large 
building. 

Insulating Materials. Perhaps one of the great- 
est problems in electric wiring has been the selec- 
tion of the correct insulating materials for electrical 
work. In order that an insulating material may 
meet with the proper consideration before trial it 
is necessary that it should be 

1. An insulator. 

2. Non-combustible. 

3. Non-absorbent. 

4. Non-hygroscopic. 

There are many insulators and insulating mate- 
rials now in use which are apparently immune from 
shortcomings in this respect, but a close examina- 
tion will reveal the fallacy which a rigid test would 
make certain. In the wiring world insulating ma- 
terial is used for switchboards, insulators, and in- 
sulation of the following materials: Marble, slate, 
porcelain, glass, mica. 

The marble and slate are used for switches, panel 



AND SWITCHBOARDS 147 

boards and switchboards. The marble is entirely 
used for switchboards. The mica is employed for 
the covering of cutouts and in a compressed form 
for sockets, etc. The porcelain and glass are em- 
ployed for general insulating purposes. The cov- 
ering of wires differs from this, in that it consists 
of rubber or gutta-percha, but the strict require- 
ments for insulation whether of wire, switches, 
switchboard or other devices are not any too high 
where special work is to be done. 

Special Insulation. In damp places, where mois- 
ture is constantly soaking in to all materials, such 
as dye houses, breweries, stables, pulp mills, laun- 
dries and acid manufactories, where fumes are ex- 
ercising a deleterious effect, special insulation is 
required on wires, which is described thoroughly 
in the following paragraph: 

The wire must have a solid insulating covering 
of at least -^ of an inch in thickness, and this cov- 
ered \vith a strong and tightly fitting braid. It 
must be difficult to burn or ignite and must possess 
insulating power sufficient to show I megohm after 
exposure through submersion to the action of water 
for two weeks, at a temperature of 70 degrees F., 
or after three days' exposure through submersion 
to the action of lime water and the passage of a 
current of 550 volts pressure for three minutes. 
It is necessary in addition to expose such wire to 
the direct action of those liquids or fumes to which 
it will be subjected. 

Concealed and Exposed Work. Wiring that is 



148 ELECTRIC-WIRING, DIAGRAMS 

either concealed or exposed represents the two 
cases where the allowance of current for the wires 
is different for the same amount of lighting. By 
this is meant that a wire of a given number of cir- 
cular mils cannot carry as much current for con- 
cealed work as for open or exposed work. 

In exposed work the air freely circulates around 
the wire and its radiating power is not limited by 
being surrounded by conduit or moulding. Such 
radiation as generally occurs takes place through 
the insulation into the outer air: 



Concealed wires in conduit. 


Open work on insulators. 


Gauge No. 
B. &S. 


Amperes 
allowable. 


Gauge No. 
B.&S. 


Amperes 
allowable. 


oooo 


218 


oooo 


312 


ooo 


181 


ooo 


262 


00 


150 


oo 


22O 


o 


125 


o 


185 


I 


105 


I 


156 


2 


88 


2 


131 


3 


75 


3 


no 


4 


63 


4 


92 


5 


53 


5 


77 


6 


45 


6 


65 


8 


33 


8 


46 


10 


25 


10 


32 


12 


17 


12 


2 3 


14 


12 


14 


16 



AND SWITCHBOARDS 



149 



The relation of current to insulation resistance 
has also been established by law as regards in- 
surance. The insulation resistance of the mains, 
feeder branches, etc., must not fall below a certain 
figure of at least 100,000 ohms. The entire wiring 
installation must not represent less than the insula- 
tion resistance given in the following table : 



Amperes. 


Insulation 
resistance. 


Amperes. 


Insulation 
resistance. 


10 


4,000,000 


200 


2OO,OOO 


25 


l,6oo,OOO 


4OO 


100,000 


50 


800,000 


800 


50,000 


IOO 


400,000 


1, 6OO 


25,000 



The manner of development of the table is quite 
evident after a slight examination of the relation- 
ship of the figures to each other. The basis is 4 
megohms for 10 amperes, which would mean a 
corresponding sub-division of the resistance for 
any other greater current. For 20 amperes the in- 
sulation resistance is one-half, for 50 amperes one- 
fifth, etc., as indicated. 

Many detailed requirements have been estab- 
lished by practice relating to the essential elements 
of a wiring equipment. They relate to such im- 
portant articles as switches, cutouts, fixtures, etc. 
As regards the last, particular attention must be 
paid to the question of insulation resistance, where 
the fixtures supply gas as well as electricity. In 



150 ELECTRIC-WIRING, DIAGRAMS 

this case the fixture is insulated from the gas pipes 
or ground connection by means of an insulating 
joint. The requirements read as follows : " Insu- 
lating joints to be approved must be entirely made 
of material that will resist the action of illuminat- 
ing gases, and will not give way or soften under 
the heat of an ordinary gas flame. They shall be 
so arranged that a deposit of moisture will not de- 
stroy the insulating effect, and shall have an in- 
sulating resistance of 250,000 ohms between the gas 
pipe attachments, and be sufficiently strong to resist 
the strain they will be liable to in attachment." 

Perhaps the most fruitful cause of grounds and 
short-circuits may be found in fixtures and sockets 
unless the utmost care is taken during their in- 
stallation to remove such possibilities by strict 
adherence to the observed code. 

Grounded Wires. When it becomes necessary 
to ground wires, when lightning arresters are in- 
stalled or protective devices are employed for tele- 
graph, telephone, fire, district messenger, and bur- 
glar alarms or their equipment, the ground wire 
must be connected to a gas or water pipe and 
connection made beyond the first joint by solder- 
ing. If such a ground connection is impossible a 
ground must be made by means of a metallic plate 
or a collection of loose wires or pipes buried in 
moist earth. The ground wire in this case must 
not be smaller than a No. 16 B. & S. and must be 
supported as though it were a high potential wire 
to the final earth connection. The protective de- 



AND SWITCHBOARDS 151 

vice is of an electromagnetic character and saves 
the circuits to which it is connected from a sudden 
rise of current and pressure due to the crossing of 
signaling and message-conveying wires with power 
or electric light circuits. It is inclosed in a water- 
proof metallic case and is placed outside the build- 
ing, or if placed inside, the wire leading into it 
through the wall must be carefully protected by 
approved insulating bushing. A very useful solu- 
tion for soldering wires may be made up from the 
following formula. It is recommended that after 
use the joint be carefully wiped to remove all traces 
of the acid and thereby prevent subsequent cor- 
rosion : 

Solution of zinc saturated 5 parts. 

Glycerine i part. 

Alcohol 4 parts. 

The solution of zinc is obtained by taking a 6 
oz. bottle and half filling it with hydrochloric acid. 
Then slowly drop in pieces of granulated zinc until 
the ebullition ceases. The solution then obtained 
corresponds to the 'first item of the formula just 
given. The joint is first heated with a blow-pipe 
or soldering iron after being carefully cleaned to 
expose the bright metal and the solution is applied 
with a stick and the solder will immediately flow 
freely. 

A very good plan is to follow a certain system 
as regards the position of every light in the build- 



152 ELECTRIC-WIRING, DIAGRAMS 

ing. Such a plan may be embodied in the form of 
what could be called " A Distribution Sheet " on 
the following order: 



DISTRIBUTION SHEET. 







No. of 


No. of 


No. of 








lights i. 


lights 2. 


lights 3. 


a 


t/5 




bb 




w 


bb 




S 


bb 




t 




"3 


* 


c 




^ 


c 




*u 






"^ 


pwj 


_o 






^""i 


^j 


^ 


^ 


4-> 


*^J 


* ] 


^_ 


ctf 


"3 
u 


fe- 


U 


ed 


CO 


'v 
U 


1 


CO 


"C 
U 


C^ 


CO 





2 


I 





I 


I 


2 





I 


O 


3 


o 


6 


I 


2 


I 





o 





2 





3 





I 


6 




3 
























4 
























5 
























6 
























7 























The idea of this sheet is to conveniently locate 
the position of all lights for ready reference and to 
hold the plan of the wiring in as explicit and con- 
densed a form as possible. The importance of this 
cannot be overestimated when the wiring of a 20- 
story building is considered with its numerous 
outlets. In order to facilitate the work an outlet 
sheet is convenient to use. It is of a much simpler 
character than the above and may be. laid out in 
this form: 



AND SWITCHBOARDS 



Floor. 


Outlets. 


Purpose. 


I 


10 


Lighting. 


2 


8 


Lighting. 


3 


6 


Lighting. 


4 


7 


Lighting. 


5 


5 


Lighting. 


6 


9 


Lighting. 


7 


2 


Motors. 


8 


3 


Lighting. 


9 


6 


Lighting. 


10 


4 


Lighting. 



In laying out the position of the conduit, the 
exact knowledge of the position of each outlet and 
junction box is a matter of great importance. Mis- 
takes in the wiring plan in this respect on a big 
job may mean considerable delay, confusion and 
expense. Both these sheets may be extended to 
cover any number of floors, and from them esti- 
mates can be prepared for future work as regards 
labor and material. 

It is often the custom to estimate on conduit 
jobs, whether open or concealed, as well as mould- 
ing and insulator work, at so much per outlet, or 
so much per lamp completely equipped. In any 
case a list of the material required must be pre- 
pared and the cost of labor, to form a clear con- 
ception of the absolute cost. The items to be 
included in this list are based upon the character 
of the work, whether insulator, cleat, moulding or 



154 ELECTRIC-WIRING, DIAGRAMS 



conduit. In each case various essentials are differ- 
ent, particularly when concealed work is done. 
In this case the estimate must cover the additional 
cost of labor involved in ripping up floors, grooving 
the walls and cutting out a place in the walls for 
panel boards. 

Panel Boards. In general house wiring the cir- 
cuits are all led to a given point on one floor if the 
floor is small, or, if it is large, several of these 
points are employed at which panel boards are in- 
stalled. Panel boards are merely slate boards on 
which small switches are systematically arranged 
for the control of the branch circuits on the floor 
and on which the fuses controlling those branches 
are mounted. 

They are built for two and three-wire mains 
(Figs. 57 and 58) with branches on both sides of 




FIG. 57. Panel Board for Two-wire System. 



AND SWITCHBOARDS 




FIG. 58. Panel Board for Three-wire System. 

the mains. In the illustrations are shown two 
panel boards as described, one for a two-wire sys- 
tem with two wire branches, the other for a three- 
wire system with two wire branches. In many 
cases a main switch is also mounted so as to give 
control to the entire floor or section of the floor as 
the case may be. In many respects these panels 
might be aptly termed secondary switchboards as 
they control the circuits at the points of distribu- 
tion. 

UNDERWRITERS' REQUIREMENTS REGARDING 
SWITCHBOARDS AND PANEL BOARDS. 

Switchboard : 

o. Must be made of non-combustible non-absorp- 
tive insulating material, such as marble or slate. 



156 ELECTRIC-WIRING, DIAGRAMS 

b. Must be kept free from moisture, and must 
be located so as to be accessible from all sides. 

c. Must have. a main switch, main cutout and 
ammeter for each generator. Must also have a 
voltmeter and a ground detector. 

d. Must have a cutout and a switch for each 
side of each circuit leading from board. 

Tablet and Panel Boards : 

The following minimum distance between bare 
live metal parts, bus-bars, etc., must be main- 
tained between parts of opposite polarity, except 
at switches and link fuses, as follows : 

When mounted on the same surface 0125 volts, 
5 inch; 126-250 volts, i| inch. W 7 hen held free in 
the air 0-125 volts, \ inch; 126-250 volts, f inch. 

Between parts of the same polarity: 

At link fuses 0-125 volts, \ inch ; 126-250 volts, 
f inch. 

At switches or inclosed fuses, parts of the same 
polarity may be placed as close together as con- 
venience in handling will allow. 

It should be noted that the above distances are 
the minimum allowable, and it is urged that greater 
distances be adopted wherever the conditions will 
permit. 

The spacings given first apply to the branch 
conductors where inclosed fuses are used. 

The spacings given second apply to the distance 
between the raised main bars, and between these 
bars and the branch bars over which they pass. 

The spacings given third are intended to pre- 



AND SWITCHBOARDS 157 

vent the melting of a link fuse by the blowing of an 
adjacent fuse of the same polarity. 

For further and more detailed reference to the 
requirements of the National Board of Fire Under- 
writers the National Electrical Code must be con- 
sulted. A copy of this may be obtained from the 
Fire Underwriters of any large city. 

The routine work of a wiring problem is plain 
sailing, but the difficulties and unexpected expenses 
arise when special positions are required for lights 
and switches. 



158 ELECTRIC-WIRING, DIAGRAMS 



CHAPTER VIII 

THE LIGHT OF INCANDESCENT LAMPS. THE POWER CON- 
SUMED BY LAMPS PER CANDLE POWER. CANDLE POWER 
AND COAL. EFFECT OF LOW PRESSURE ON LIGHT. 
EFFECTS OF GLOBES ON LIGHT. SIZE OF ROOM AND 
NUMBER OF LIGHTS. USE OF SIDE LIGHTS AND CHANDE- 
LIERS. COLOR OF ROOM DECORATION AND THE LIGHT- 
ING. 

Light of Incandescent Lamps. The importance 
of considering in its proper aspect the light of 
lamps of the incandescent type, is due to the re- 
lationship between voltage and candle power in 
these lamps. To obtain the maximum light from 
the minimum power is not so much an object as 
to obtain durability or lasting qualities in the lamp. 
As lamps grow old they deteriorate and the light 
grows dim, so that to obtain the correct candle 
power such an accession of power is required as 
to make the production of such light a most un- 
economical proceeding. The efficiency of a lamp, 
or the relation between the light it gives and power 
it consumes, are matters of the utmost importance 
not only in its construction but in its utilization as 
well. In speaking of power, both volts and am- 
peres must be considered, therefore, when greater 
or less voltage is supplied to lamps or when the 



AND SWITCHBOARDS 159 

percentage of the normal is below or above 100 
per cent., the power consumption and the candle 
power vary accordingly. Tables have been pre- 
pared by many manufacturers covering these feat- 
ures, but they generally relate to the ratio of 
candle power to watts. This is given in the form 
of a given number of watts per candle power, and 
the average lamp consumes from between 3 to 4 
watts per candle power. In the following table 
some figures are given expressing the relationship 
between light and power for a consumption of 
power which varies from i to 4 watts per cp. : 

TOTAL WATTS =64. 



Watts per cp. 


Total cp. 


I.O 


64.00 
42.66 


2.0 

2-5 


32.00 
25.60 


3-5 
4.0 


2I -33 
18.29 
16.00 



The practical basis is about 3.1 to 3.5 watts per 
candle power and on this relationship of power to 
light the following lamps, their candle power and 
wattage are given : 



160 ELECTRIC-WIRING, DIAGRAMS 

WATTS PER CP. =3.1. 



Candle power. 


Total watts. 


IOO 


310 


50 


155 


32 
16 
8 


99.2 
49.6 
24.8 



These figures are bound to vary after the lamps 
have been in use a certain number of days. After 
prolonged use the lamps appear smoky and give 
a poor and inefficient light, which is due to the 
increased resistance of the filament. But if more 
than the normal pressure is supplied the light 
though brilliant is in the end very expensive be- 
cause of the subsequently rapid injury to the lamp 
and its exceedingly poor return for the power. 
The normal voltage of a lamp therefore changes ; 
gradually rising as the life of a lamp goes on and 
thereby increases the watts per candle power and 
drops the efficiency lower. A lamp lasts much 
longer if the voltage is a little lower, and acts more 
satisfactorily as a light producer in the end as far 
as the expense for lamps is concerned. But the 
danger lies in the voltage being too low and the 
light too dim. Then the practical efficiency of the 
lighting plant is affected. If the drop in the wires 
cause this, the wiring is a failure, but if the dynamo 
pressure is too low it should be increased. As an 



AND SWITCHBOARDS 161 

illustration of the enormous practical importance 
of this fact in electric wiring and electric lighting, 
take a no- volt lamp of 16 cp. and run it below its 
normal pressure. Let the voltage be limited to 
about 104.5 to IO 5-5 volts and measure the candle 
power. It will not exceed 12 cp. In other words, 
a slight reduction in voltage to the lamp means a 
great drop in candle power, and if ten or twenty 
thousand dollars are spent to obtain a certain 
amount of candle power and 25 per cent, is wasted 
by low pressure the remaining candle power is ob- 
tained at a heavy expense. The only item to 
counterbalance this is the saving in lamp cost. 
The saving in lamps must therefore be balanced 
up against the value of the lost light on such a 
basis. In all probability a 25 per cent, cut in candle 
power will not pay when compared with the cost 
of lamp renewals. Take a 1,000 light no volt plant 
at an estimated cost of $10,000. If 25 per cent, of 
the light is wasted in order to save lamp renewals 
then the light of 250 lamps, at a pressure of about 
106 volts, is practically thrown away. The cost 
of 1,000 lamps is about $200 at 20 cents apiece, or 
higher, as the case may be according to prevailing 
market rates. The value of the light of 250 lamps, 
if supplied outside, is at least $100 a month. Esti- 
mating the life of these lamps at 600 hours and 
burning them 5 hours a day, it would mean 130 days 
or about a four months' steady run before they com- 
pletely failed. If run at a low voltage they might 
last longer and only mean renewals twice, instead of 



162 ELECTRIC-WIRING, DIAGRAMS 

three times a year. The cost of this is about $400, 
which can be compared with the $1,200 worth of 
light thrown away by low voltage. If the coal pile 
alone is considered, it will be seen that the amount 
of coal required for 1,000 lights at 5 Ibs. per horse 
power hour would be, on the basis of 12 lamps per 
horse power, as follows : 

If 12 lamps = 5 Ibs. per hour, 
then 1,000 lamps = 83 X 5 = 415 Ibs. per hour. 

On the estimate of 5 hours' lighting a day the total 
weight of coal consumed amounts to 5X415 = 
2,075 Ibs. or about one ton. This coal may cost 
various prices per ton, but if $4 is taken as a fair 
price for good coal, then the expense in this direc- 
tion amounts to about $1,200 for 300 working days 
in the year. Of this amount 25 per cent, or $300 
worth is systematically thrown away by the low 
voltage being employed to save lamp wear. Each 
lamp renewal costs $200, and it seems at the best 
all that can be done is to reduce the number of 
lamp renewals from three to two per annum. This 
means a saving of only $200 in lamps as compared 
with $300 worth of coal which is burned and 
wasted. The depreciation of the plant is not con- 
sidered nor the interest on the investment, nor 
the fact that the labor paid for each year could do 
the extra lighting without extra trouble, etc. An- 
other feature of the case is the fact that if the light 
is poor extra lighting must be done to supply the 
required illumination, as the practical basis for 



AND SWITCHBOARDS 



163 



ordinary rooms should be about 16 cp. for every 
50 or 75 square feet of floor space, depending upon 
the tone of the decorations and wall paper. The 
appended table, giving figures taken from the rec- 
ords of the largest manufacturers of lamps in the 
United States with additions by the author, shows 
the fall of efficiency with the voltage and the heavy 
reduction in the illuminating power of the lamp : 

RATE OF 3.1 WATTS PER CP. 



Percentage of 
the correct lamp 
pressure. 


Percentage of 
the correct can- 
dle power. 


Watts con- 
sumed per cp. 


Candle power 
of a loocp. 
lamp. 


90 


53 


4.68 


53 


9 1 


57 


4.46 


57 


92 


61 


4.26 


61 


93 


65 


4.1 


65 


94 


69-5 


3-9 2 


6 9-5 


95 


74 


3-76 


74 


96 


79 


3-6 


79 


97 


84 


3-45 


84 


98 


89 


3-34 


89 


99 


94-5 


3.22 


94-5 


IOO 


100 


3- 1 


IOO 


IOI 


1 06 


2.99 


1 06 


102 


112 


2.9 


112 


103 


118 


2.8 


118 


104 


124.5 


2 -7 


124-5 


105 


131-5 


2.62 


I 3 I -5 


I O6 


138.5 


2-54 


138-5 



The figures show that in the case of a TOO cp. 
no volt incandescent lamp between the voltages 



i6 4 ELECTRIC-WIRING, DIAGRAMS 

of 99 and 116.6 the candle power varies from 53 to 
138.5 or almost as I is to 3. 

The various types or shades and globes also 
govern the amount of effective candle power ob- 
tained. It is a well-known physical fact that the 
various colors of glass are more or less absorptive, 
and may reduce the amount of useful light to such 
a degree as to render useless efforts to better it. 
The following figures relate to this fact with re- 
spect to the globes and the degree of absorption : 



Character of glass. 



Percentage of wasted light. 



Ordinary pane glass 
Cut or pressed glass. 

Ground glass 

Opalescent glass 

Red glass 

Blue glass 



about 10 per cent, 
from 10 to 15 per cent, 
from 25 to 40 per cent, 
from 25 to 50 per cent, 
from 30 to 60 per cent, 
from 15 to 30 per cent. 



The depth of color in the glass is a prime factor 
in determining the degree of absorption. A great 
deal of candle power can be produced, and wasted 
by the use of poor globes, thus nullifying advan- 
tages of good wiring and regulation. 

Choosing Globes. In choosing globes several 
points must be taken into consideration which 
might be tabulated in the following manner: 

i Cost of globes. 

2 Diffusion of light. 

3 Degree of absorption. 



AND SWITCHBOARDS 165 

4 Artistic design. 

5 Fragility. 

By the use of a little common sense the selection 
of such important articles can be made with a defi- 
nite purpose in view. Many of the best looking 
globes are poor light transmitters and the con- 
verse. As a general rule the cost and design are 
the predominating factors, whereas the effective 
diffusion of the light and the degree of absorption 
are perhaps of more importance from an economical 
and practical standpoint in the long run. 

The area of the lighted room as well as the 
height of the ceilings next lead to the determina- 
tion of the answer to the question : " How shall the 
lamps be distributed and how many must be used? " 
Take a room 20 feet in length by 15 feet in width 
and 12 feet high. The floor area is 20 X 15 = 300 
square feet; and the wall area equals 15 X 12 X 2 = 
360 added to 20 X 12 X 2 = 480 or a total of 840 
square feet. In order to illuminate this room suc- 
cessfully side lights must be employed and a chan- 
delier. Allowing one 16 cp. lamp for every 50 
square feet, in the case of a parlor or drawing room 
a six-light chandelier is required. If side lights 
exclusively are employed the figures used with 
reference to the walls would be 100 square feet per 
16 cp. lamp or an allowance of about 8 lamps. 
When the lighting is divided up between the side 
lights and chandelier about four side lights and 
four chandelier lights are the best to employ. This 
would mean the utilization of about 100 cp. from 



i66 ELECTRIC-WIRING, DIAGRAMS 

the chandelier after it passes through the globes 
and 130 cp. from the side lights if used exclusively; 
or a total amount of candle power equal to at least 
130 if distributed throughout the room. It is there- 
fore evident that the distribution of the light is of 
more importance than the quantity, and a great 
deal of power can be ineffectively used to light a 
room where one-half as much, consumed in prop- 
erly arranged lights, would give greater satisfac- 
tion. The absorptive power of the globes must be 
considered in practical lighting particularly where 
it is necessary to bring out decorative effects at 
night. 

If the general tone produced by the decorators' 
art in fine apartments is blue, pink or red, the light- 
ing must be done by choosing positions and globes 
to augment this effect and not to produce a dis- 
agreeable impression through inattention to such 
details. If red, blue or other colored globes are 
employed and full illumination is required the lost 
percentage of light must be added in the number 
of lamps or the candle power of the globes. 

It is well for those desirous of making of wiring 
an art as well as a trade to study the requirements 
of the business and social world in order to succeed 
in meeting the demands they make upon the con- 
tractor. The great dry-goods and department 
stores, the public buildings, the theatres, the 
churches and the home these are not easy prob- 
lems that relate alone to the putting in of wires. 
They call for greater knowledge, which in its high- 



AND SWITCHBOARDS 167 

est form goes hand and hand with the dictates of 
art and fashion. To produce not merely light, but a 
uniform light is the main idea, and in great audito- 
riums a careful study of conditions is the only way 
of meeting with any degree of success. The candle 
power is dependent entirely upon the voltage and 
to keep this up to the standard as well as to control 
the groups of lights, or, in other words, to obtain 
control and regulation of the light with one or more 
dynamos in lighting plants, the switchboard has 
been universally adopted. 



i68 ELECTRIC-WIRING, DIAGRAMS 



CHAPTER IX 

SWITCHBOARDS AND THEIR PURPOSE. THE PARTS OF A 
SWITCHBOARD. CONNECTIONS OF A SHUNT WOUND 
GENERATOR. THE CIRCUIT BREAKER. THE RHEO- 
STAT. CONNECTIONS OF A COMPOUND WOUND GENERA- 
TOR. FUSES. CONNECTIONS OF TWO SHUNT WOUND 
GENERATORS AND SWITCHBOARD. EQUAL PRESSURES 
FOR BOTH DYNAMOS. THE BUS BARS. BACK VIEW OF 
SWITCHBOARD SHOWING WIRING CONNECTIONS FOR TWO 
SHUNT MACHINES. CONNECTIONS OF COMPOUND WOUND 
MACHINES SHOWING BUS BARS AND EQUALIZER BAR IN 
SERVICE. OVER COMPOUNDING. THE SERIES WINDING 
AND ITS PURPOSE. 

Switchboards. As the switchboard represents 
the connections which are made to obtain con- 
venient control of the circuits and in the case of 
several generators to effectually combine and direct 
their output, it is supplied with switches, meas- 
uring instruments, circuit-protecting devices and 
regulating devices. These may be considered in 
their order 

i Switches, 

2 Meters, 

3 Circuit breakers, 

4 Rheostats, 

further additions being merely secondary acces- 
sories not required by the code. 



AND SWITCHBOARDS 169 

A switchboard cannot be designed until the cir- 
cuits leading to and from it have been carefully 
drawn out so that the number of switches, meters, 
circuit breakers and rheostats are fully known. It 
is not the practice to put up a board and then 
attach the wires, because the stony character of 
the material calls for careful drilling, and in addi- 
tion, the size of the stone or marble slab must be 
determined from the apparatus to be attached to it. 
This can be obtained from the schedule or list of 
the circuits and the character of the generators to 
be connected. 

Connections of a Shunt Wound Generator. 
The essential connections of a shunt wound gene- 
rator relate to the armature and field connections 
and the devices connected to them either for pur- 
poses of regulation, protection or measurement. 

As shown in the illustration (Fig. 59) the con- 
nections of a shunt wound generator call for a 
rheostat in series with the field 'circuit ; a main 
switch which controls the entire current supply 
and the two essential measuring instruments, an 
ammeter and a voltmeter. The ammeter is in 
series with the main circuit and indicates the total 
flow of current. The voltmeter is in multiple with 
the main circuit and indicates the voltage at the 
switchboard. 

Protection. The circuits are protected individu- 
ally by means of fuses and collectively by means of 
a circuit breaker. There is a main switch, which, 
when opened, cuts off all communication between 



170 ELECTRIC-WIRING, DIAGRAMS 

the dynamo and lighting circuits. This is also 
fused and acts as a protective device, but the de- 
vice which is accepted as most reliable and con- 



VOLTMETER AMMETER 




FIG. 5^). Connections and Accessories of a Shunt Wound Dynamo. 

venient is the automatic electro-magnetic circuit 
breaker. 

Circuit Breaker. An automatic circuit breaker 
consists of a helix of heavy copper wire through 
which the full volume of the current circulates. 
This helix attracts an iron core whose pull is re- 
sisted by a powerful spring. The magnetic pull 
and the spring balance each other under ordinary 
conditions. When a heavy short circuit occurs, the 
pull of the helix, and consequently of its core, be- 



AND SWITCHBOARDS 171 

comes so great that the spring is overcome and a 
latch gives allowing the main line switch to fly 
open. This switch is so constructed that it opens 
instantaneously and without arcing and acts as the 
most efficient circuit protector in daily practice. 

Rheostat. The rheostat is in series with the field 
winding and the main line is tapped at both poles 
to supply it with current. An examination of the 
sketch will show that the field and rheostat in 
series, are together in multiple with the larmature 
terminals, so that the regulation of the dynamo 
can be readily accomplished by following; the con- 
nections and mounting the rheostat on the switch- 
board. The rheostats in general use for switch- 
board connection are of the enamel type; that is, 
composed of iron or composition wires buried in 
enamel and attached to a flat metallic frame with 
considerable radiating surface. They occupy little 
space and have added greatly to the equipment of 
the switchboard. 

Connections of a Compound Wound Generator. 
The sketch (Fig. 60) shows a difference between 
the connections only in so far as the series winding 
is concerned. The same devices are in use, namely, 
a rheostat, a circuit breaker, a main line switch and 
meters to register current and voltage. The series 
winding also carries the total current of the lamps, 
and final connections must be made to this effect. 
On nearly all switchboards there is provided a 
pilot lamp, which gives the light or pressure 
straight from the dynamo, and in addition a ground 



172 ELECTRIG-WIRING, DIAGRAMS 

detector which is merely a lamp with one leg 
grounded and a push button in circuit to show the 
presence of a ground. It is so constructed that 



VOLTMETER AMMETER 




FlG. 60. Connections and Accessories of a Compound Wound 
Dynamo. 

both legs of the circuit can be tested. The switch- 
board of both machines can be so designed that 
the street service can be turned on by use of a 
double poled and double throw switch. The com- 
pound wound generator is almost exclusively em- 
ployed in private plants and for street railway work 
on account of its automatic regulation. 

Fuses. The fuses in general use for switch- 
boards are of the approved non-arcing type. Fuses 



AND SWITCHBOARDS 173 

of this character are surrounded by an envelope or 
tube of incombustible material, within which the 
melting or volatilization of the fuse may take place 
without the spattering of metal or the deposition 
of fumes on the polished switchboard. In total 




FIG. 61. Diagrammatic Connections of Two Shunt Dynamos in 
Multiple. \ 

these items comprise the essentials and accessories 
of an ordinary switchboard for a single shunt or 
single compound wound machine. 

Connecting Two Shunt Wound Dynamos. The 
method of connecting two shunt wound machines 
in multiple is shown in the sketch (Fig. 61). A 



i 7 4 ELECTRIC-WIRING, DIAGRAMS 

certain amount of care must be exercised, because 
both are generators of electromotive force, and in 
consequence conditions result which would be dan- 
gerous if disregarded when both machines are in 
operation. Both machines may run as follows : 

First Both at equal pressure. 

Second Both at unequal pressure. 

Third One as a dynamo and one as a motor. 

In order to have both run at an equal pressure, 
first one is allowed to run until its EMF. is correct, 
the switch of the other machine being open, then 
the process covers the following as regards the 
other. The second machine is brought up to 
speed and its pressure made to tally with the first 1 
machine. This is accomplished by means of the 
regulating device or rheostat, whose action is 
recorded by the voltmeter. By means of these two 
devices the pressures are made to correspond with 
great exactness, before the main switch from the 
second dynamo is thrown in. When both dynamos 
are of equal pressure the main line switch is thrown 
in and this immediately calls upon the two dynamos 
for power. If they are alike in construction the 
variation in load will not be very great, but this 
is not apt to be the case, and the pressure of each 
must be again regulated until they are approxi- 
mately correct. This is an operation requiring 
some skill and practical experience before it is 
done quickly and without risk. 

Unequal Pressures. The risk mentioned is that 
due to the unequal pressures, which cause the loads 



AND SWITCHBOARDS 175 

on the machines to be unequal and thereby throws 
too much on one and too little on the other. This 
is apt to cause overheating of the armature and if 
sustained over a long period a possible burn-out. 
Another danger is present however, and this is due 
to the fact that one may run as a motor if its press- 
ure falls very far below the other. 

Under these circumstances the fields will remain 
as before, and the dynamo will continue to run in 
the same direction as a motor, because the current 
is now entering the armature in the opposite direc- 
tion. This experiment can be readily tried with a 
small experimental shunt dynamo. The machine 
may be used as a generator with separately excited 
fields. If a reverse current is suddenly switched 
into the armature it will continue to run in the 
same direction as a motor. In the sketch (Fig. 62) 
two bus bars are employed to which the main line 
switch is connected and from which the pressure 
at the generators is readily obtained. The entire 
regulation in the case of two or more shunt wound 
dynamos running in parallel consists in looking 
out for the equal distribution of the load by means 
of the regulating rheostats. In the sketch is shown 
the appearance of the switchboard with all the in- 
struments and switches mounted. Two push but- 
tons are used for testing for the pressure of each 
dynamo respectively. The bus bars are also in 
evidence, and in this case they simply consist of 
solid bars of pure copper to which all three switches 
are joined by copper bars. 



176 ELECTRIC-WIRING, DIAGRAMS 

It is easy to see this connection in practice in 
the other sketch. First the two dynamo switches 
which convey the current from the dynamos to 




VOLTMETER 
BUTTON FOR EACH DYNAMO 



FIG. 62. Front View of Switchboard of Two Shunt Dynamos in 
Multiple. 

the bus bars ; then the main line switch through 
which the total current passes to the lighting or 
motor circuits. Each of the dynamo circuits has 
in series with it a circuit breaker, which protects 
the dynamo to which it is connected from an ab- 
normal load. There are non-arcing fuses mounted 
on the switches as an additional protection. It is 
also possible to have but one circuit breaker in 
the main line and thereby dispense with the two 
used in connection with the dynamos, but indi- 



AND SWITCHBOARDS 



177 



vidual protection for each machine is by far the 
best policy in general switchboard design. The 
use of two voltmeters instead of one is also the 
best practice although not absolutely necessary. 

The rear view of the switchboard is shown in 
the next sketch (Fig. 63) with the connections to 




FIG. 63. Back View of Wiring Connections of Two Shunt Dynamos 
in Multiple. 

the different devices on the face of the board. In 
all cases where a single voltmeter is used with 
push button contacts from each dynamo care must 
be taken that each pole is connected right or a 
short circuit will result at the voltmeter binding 
posts or poles. The main circuit from each dynamo 



178 ELECTRIC-WIRING, DIAGRAMS 

runs through the ammeter in series with which is 
the circuit breaker as shown. Two conductors of 
flexible cable lead the current from each dynamo 
respectively into its controlling switch and thence 
into the bus bars. From the bus bars through 
the main switch the current is led out to the dis- 
tributing circuits. In this case the circuits on the 
different floors are not individually controlled from 
the switchboard. If it is necessary to do this, the 
switchboard becomes a little more elaborate and 
the switches controlling the different floors must 
be shown on the face and back of the board. 

The control of different floors by means of the 
switchboard is required in complete equipments. 
A case of this kind is exhibited in the illustration 
(Fig. 64) where six separate circuits, each with 
its main switch, compose one section of the switch- 
board. 

The back (Fig. 65) and front appearance are 
shown, with all apparatus mounted in its place, 
and all wiring connections complete. It must be 
understood that if there are many changes in the 
load the switchboard will not help to regulate it. 
It only serves as a convenient place on which to 
group the different devices and at which to con- 
centrate all the principal circuits. If the variation 
of load due to changes in the number of lights on 
the different floors is very marked, it will be 
necessary to regulate by the rheostat as often as 
required. In some plants of this description this 
is inevitable and represents one of its greatest 



AND SWITCHBOARDS 



179 



drawbacks. If this rheostatic regulation is not 
attended to, the load upon the machines will dis- 



VOtTMETER 



VQLJMETER 




RHEOSTAT 



DYNAMO 
SWITCH 



FIG. 64. Front View of Switchboard with Two Shunt Dynamos in 
Multiple, Showing Mains to Various Floors. 

tribute itself unevenly, and may affect their speeds 
if the difference in balance is too great. In this 
case an overload would result, on either one or 



i8o ELECTRIC-WIRING, DIAGRAMS 

the other dynamo, and the circuit breaker will act, 
cutting open that circuit, as the case may be. 




FIG. 65. Back View of Switchboard with Two Shunt Dynamos in 
Multiple, Showing Wiring Connections to Mains from Bus Bars. 

The only satisfactory way in which two gener- 
ators can be run automatically with safety under 
all reasonable changes of load, and still preserve 
the pressure at its proper value, is by installing 



AND SWITCHBOARDS 181 

two compound wound dynamos, and attaching 
them in multiple to the switchboard as shown. 
Both shunt and compound wound dynamos are in- 
cluded under the technical appellation " constant 
potential machines," but they differ from each 
other, as has been previously pointed out, in their 
field windings. One has merely the ordinary shunt 
winding, the other has also a shunt winding, but 
a series winding in addition. In fact a compound 
wound dynamo, as far as its windings are con- 
cerned, consists of a series wound and shunt 
wound generator with their windings, as it were, 
superposed upon each other. 

The Equalizer. The automatic regulation is ac- 
complished by the series coil, and it is therefore 
necessary when two machines of this type are 
connected in multiple to secure the correct action 
of each by means of what is commonly termed an 
"equalizer bar" (Fig. 66). This bar simply con- 
nects one brush of each dynamo to the correspond- 
ing brush on every other dynamo connected to the 
series coils. In the case represented only two 
dynamos are in multiple, and it will be seen that 
the equalizer bar in this case was from the upper 
brush of one dynamo to the upper brush of the 
other; but it will be noted that this upper brush 
also feeds into the series coil of each dynamo re- 
spectively. If this idea is carefully followed out 
the diagram will also show that the upper brush 
of each generator can send its current either into 
the series coil or into the equalizer bar. If the 



i8 2 ELECTRIC-WIRING, DIAGRAMS 

potential at each of these brushes is alike, the 
equalizer bar carries no current ; but if the pressure 
generated by one dynamo is a little higher than 



AMMETER VOLTMETERS 




FIG. 66. Diagrammatic Connections of Two Compound Wound 
Dynamos in Multiple, with Equalizer Bar Connected. 

the other, due to the fact that the speed of either 
one has diminished, or the load on one is greater 
than that on the other, then, current from this brush 
of higher potential, will flow through the equalizer 



AND SWITCHBOARDS 183 

bar into the series coil of the other dynamo. The 
effect of this is to strengthen its magnetic field, 
thereby increasing its electromotive force and in 
this manner augmenting the pressure until both 
machines in this respect are in equilibrium. But 
it is also evident that when one machine builds 
up the series coil of another in this manner, it is 
at the expense of its own, therefore as the press- 
ure of one machine rises, the pressure of the other 
machine falls until both are equalized. The equal- 
izer circuit should be closed before the other cir- 
cuits, and to accomplish this it is often the practice 
to either have a separate switch in this circuit, or 
to provide a longer blade to the middle of the 
switch shown, so as to close this first as described. 
The two main wires running across in the last 
sketch, are bus bars of heavy copper, and feed the 
main line, or supply current, to a variety of switches 
connecting with the various floors or circuits of the 
building. The equalizer should be of very low re- 
sistance, otherwise the drop through it may rise 
too high, if for any reason it ever carries a con- 
siderable volume of current. By having it of ample 
cross section, the regulation may be carried to a 
fine point. In large plants, where several thousands 
of amperes may be generated, a sudden variation 
in load will be the cause of a heavy current flow- 
ing, which might develop a heavy drop in the 
" bar," if the resistance is not low. For instance, 
a resistance of .001 of an ohm, with a current of 
loo, 1,000 and 2,000 amperes respectively, means 



184 ELECTRIC-WIRING, DIAGRAMS 

a drop of T V, i and 2 volts. This is very much 
accentuated, if the resistance of the bar is more, 
which, in some instances, it is very likely to be. 

Series Fields. The adjustment of the series coil 
is also a matter of the greatest practical impor- 
tance. The amount of current it carries may be 
too great or too small. If this is the case, it is 
now the practice to regulate with a shunt placed 
in multiple with the series winding, to vary the 
current within certain limits. 

This variation of the current is necessary be- 
cause in some instances the ampere turns of the 
series coil are too great. It is not practical to cut 
down the turns after a dynamo is completed, but 
it is very easy to shunt part of the current and 
thereby reduce the magnetic effectiveness of the 
series coils. The adjustment of the pressure of a 
compound wound dynamo is thus made possible 
within very fine limits by this means. When it 
is desirable to over-compound a generator, the reg- 
ulating of the resistance of this shunt is a rapid 
and practical process. In tests where the regula- 
tion of a dynamo is limited by specifications to a 
few volts, from no load to a full load of 500 am- 
peres, such adjustment as this is appreciated in a 
commercial as well as a scientific sense. 

Over Compounding. A dynamo is said to be 
over compounded if the series coils more than com- 
pensate for the various losses in the way of drop 
in the armature and armature reaction. A dynamo 
is over compounded, so that it will generate enough 



AND SWITCHBOARDS 185 

extra pressure to equal the drop experienced in the 
conducting wires. The theory of the compound 
wound dynamo fully covers this ground, yet it may 
be condensed into a convenient form under the 
following headings: 

PURPOSE OF THE SERIES WINDING. 

First To compensate for armature reaction 
which cuts down the useful lines of force. 

Second To compensate for the drop caused by 
the armature current flowing through the armature 
winding. 

Third When over compounding, to compensate 
for the volts drop in the main lines and feeders. 

Fourth To provide automatic regulation for all 
loads. 

The over compounding may be from 5 to 10 per 
cent, of the normal pressure, but this is largely 
governed by the percentage of drop in the wiring 
system. The method of compounding in general 
is of importance with respect to the wiring propo- 
sition, for the reason that regulation at different 
points of load if ineffective will mean poor lighting. 
Where the entire plant must be installed, as well 
as the wiring, the selection of the dynamo, whether 
shunt or compound wound, cannot be intelligently 
made unless a full knowledge of the requirements 
of such a machine are in possession of the pur- 
chaser. It is advisable to select an over com- 
pounded machine and modify the degree of the 



iS6 ELECTRIC-WIRING, DIAGRAMS 

over compounding by manipulating the german 
silver shunt attached in multiple with the series 
coil. If the resistance of this german silver shunt 
is increased, the over compounding will increase, 
that is to say, more current will flow through the 
series coils. But if the resistance of this auxiliary 
shunt is diminished, then less current flows through 
the series coils and the additional voltage they 
are the means of generating is cut down. Under 
ordinary conditions a compound wound dynamo 
simply preserves externally a uniform pressure, but 
if the drop outside will not allow of this condition 
prevailing then over compounding is resorted to 
and the building up of pressure takes place ex- 
ternally, hand in hand with the increase of the 
load. 

Street Railway Plants. Compound wound gen- 
erators are used exclusively in street railway power 
houses. In stations of this character a sudden 
change in load of from 100 to several thousand 
amperes is not an unusual occurrence, and for that 
reason the utter futility of installing any other 
class of direct current generators has been repeat- 
edly exemplified in the early history of street rail- 
way practice. The compound wound dynamo is 
the only practical solution of the lighting problem 
for private plants and street railway service, and 
its automatic regulation in well-designed machines 
leaves but little to be desired. In street railway 
service the large switchboards are well equipped 
with automatic circuit breakers to avoid burn-outs. 



AND SWITCHBOARDS 187 

The compound wound dynamo particularly re- 
quires the installation of these devices, because 
when short-circuited all the effects of an abnormal 
load are in evidence and the pressure is preserved. 

Serious damage would result if this, at times of 
terrific strain, were not relieved by means of the 
circuit breakers. It is not alone the dynamo which 
is concerned in such a case but the engine as well, 
parts of which are apt to give or at least be per- 
manently affected by an abnormal load. 



i88 ELECTRIC-WIRING, DIAGRAMS 



CHAPTER X 

GENERATORS FOR ALTERNATING AND DIRECT CURRENT LIGHT- 
ING. CHARACTER OF LIGHTING DONE. THE SWITCH- 
BOARD FOR TWO COMPOUND WOUND GENERATORS. 
CONNECTIONS TO INSTRUMENTS. SWITCHBOARD FOR 
CONTROL OF SIX FLOORS AND TWO ELEVATORS. CON- 
NECTING TWO SHUNT DYNAMOS ACCORDING TO THE 
THREE WIRE SYSTEM AT THE SWITCHBOARD. SWITCH- 
BOARDS FOR ELECTROLYTIC WORK. 

Switchboards. The immense number and variety 
of the switchboards employed for electric light and 
power purposes for both alternating and direct cur- 
rent, require some classification with regard to the 
character of the lighting as well as the type of 
generator employed. The following headings may 
prove convenient in this respect : 

SWITCHBOARD DESIGN. 
Character of generators. Character of lighting. 

1 . One shunt wound dyna- Low tension arc and incan- 

mo. descent. 

2. Two or more shunt Low tension arc and incan- 

wound dynamos. descent. 

3. One compound wound Low tension arc and incan- 

dynamo. descent. 

4. Two or more compound Low tension arc and incan- 

wound dynamos. descent. 



AND SWITCHBOARDS 



189 



Character of generators. 

5. Two or more shunt 

wound dynamos con- 
nected for the three- 
wire system. 

6. Two or more shunt 

wound dynamos con- 
nected for a combina- 
tion two and three- 
wire system. 

7. One or more series dy- 

namos each with sep- 
arate circuit. 

8. One alternator single 

phase. 

9. Two or more alternators 

single phase. 

10. One or more alternators 
two or three phase. 



Character of lighting. 

Low tension arc and incan- 
descent. 



Low tension arc and incan- 
descent. 



High tension arc lighting. 



Low tension arc and incan- 
descent. 

Low tension arc and incan- 
descent. 

Low tension arc and incan- 
descent. 



The last class of generators are employed for 
power transmission at exceedingly high pressures 
and in this respect they are better known than as 
generators for electric lighting. 

To lay out the design of a switchboard, it is ab- 
solutely necessary to become familiar with all the 
requirements of practice and the apparatus em- 
ployed for that purpose. The low tension, direct 
current apparatus differs essentially from the high 
tension, direct and alternating current. The higher 
departments of switchboard design call for an in- 
timate knowledge of the subject, and the proper 
protection and control of circuits and the care of 
the generator, whether direct or alternating, is 



igo ELECTRIC-WIRING, DIAGRAMS 

largely dependent upon the amount of skill shown 
in the construction of the switchboard. A variety 
of technical works are at the command of the reader 
and systematic visits to large power stations will 
soon develop a familiarity with the subject which 
will show the relationship existing between station 
management and switchboard design. 

A satisfactory method is to lay out the plan of 
the switchboard so that the marble or slate can be 
drilled to receive the instruments and switches. 



I CIRCUIT BREAKER CIRCUIT BREAKER, 




MAIN SWITCH 
EQUALIZER BAR 




>oo 0/ 



VOLTMETER SWITCH VOLTMETER SWITCH 



FIG. 67. Front View of Switchboard of Two Compound Wound 
Dynamos in Multiple. 



AND SWITCHBOARDS 



191 



These must then be carefully mounted and con- 
nected up according to the sketches of the back 
view. Errors can be readily corrected on the draw- 
ing board and the sketches must be carefully ex- 




FIG. 68. Back View, Showing Wiring Connections of Two Com- 
pound Wound Dynamos. 

amined to detect errors before the board is drilled. 
In the series of sketches (Figs. 67 and 68) supplied 
many items shown are more or less arbitrary. 
For instance, having the switches in the upper 



i 9 2 ELECTRIC-WIRING, DIAGRAMS 

or lower part of the switchboard, using single- 
pole or double-pole circuit breakers, controlling 
all main circuits from the switchboards or where 
they are used, etc. (see Figs. 69, 70, 71 and 72). 



D. P. CIRCUIT BREAKER 



D.P. CIRCUIT BREAKER 




ELEVATOR SW. 
FREIGHT 



EQUALIZER BAR 



EQUALIZER 
SWITCH 



VOLTMETER 
SWITCH 



VOLTMETER 
SWITCH 



ELEVATOR SW. 
PASSENGER 



o 

RHEOSTAT 



FIG. 69. Switchboard of Two Compound Wound Dynamos in 
Multiple. Switches of 6 Floors and 2 Elevators. 

It will be found that the architects' or consulting 
engineers' specifications will govern all this. If 
advice is needed, a practical switchboard manu- 
facturer is the best man to consult. 

Panel Switchboards. Not only instruments and 



AND SWITCHBOARDS 193 

switches, but finished panels can be obtained com- 
plete from the manufacturer. These panels are in 
themselves small switchboards although sold under 
the names of generator panels, rheostat panels, 



VOLTMETER 




D. P. C. B. 
O O 



-OF.O 




O O 



c i c c rc 



i 



i r 



C fC C C CBUSIB 



O 



CKCX 



iinn ? 



C ( I 



<r 



tfc 




J) C 

EL.SW. 

OpQ 



FIG. 70. Back View of Switchboard, Showing Connections to 
Equalizer Bar, Switches and Meters. 

load panels, feeder panels, fuse panels and blank 
panels. These panels are about 5 feet by 2 feet, 
although the feeder and fuse panels are about one- 
half the length of the others. 



i 9 4 ELECTRIC-WIRING, DIAGRAMS 

The generator panels are made for either a 
single generator or designed so that further addi- 
tions will allow of more than one generator to be 
run in multiple. The generator panel consists of 



CIRCUIT BREAKER 



VOLTMETER AMMETER 

o t? 



CIRCUIT BREAKER 




FIG. 71. Two Shunt Dynamos Connected According to the Three- 
wire System. 

measuring instruments, ground detector, circuit 
breaker, switch and generally a lamp and shade. 
They are made of a capacity of from 200 to 3,000 
amperes. A rheostat panel is used for the purpose 
of mounting the rheostat on its back, the contacts 



AND SWITCHBOARDS 195 

and arm appearing in the front. The load panel 
carries voltmeter and ammeter ; the voltmeter of 
the illuminated dial dead beat differential type; 
the ammeter also with illuminated dial. The volt- 



VOLTMETEF VOLTMETEF 



I | | I I I I I 



ccc ccc 




ooo ooo 

SWITCHES 



ill 



m m m ? 
I 1 ? ? ? ? i 



tt? 




FIG. 72. Back View of Connections of Two Shunt Dynamos Oper- 
ating on the Three-wire System. 

meter is mounted on a swinging bracket and is 
used : first, for measuring the potential of the bus 
bars ; second, for measuring the difference between 
the potential of the bus bars and that of the dynamo 



196 ELECTRIC-WIRING, DIAGRAMS 

about to be connected. When this last is being 
accomplished the voltmeter is swung out at right 
angles to the switchboard and the dynamo tender 
adjusts the rheostat until the voltmeter reads zero. 
When the differential voltmeter reads zero the 
generator switch is thrown in. Load panels are 
built of a capacity reaching from a few hundred 
to 15,000 amperes. The feeder panels carry am- 
meters, circuit breakers and switches. The circuit 
breakers may be single or double-pole, the am- 
meters one or many according to the capacity of 
the panel, which is naturally governed by the car- 
rying capacity of the switches. Only switches may 
be mounted in special cases on the feeder panels 
where many circuits must be accommodated in a 
limited space. The fuse panels are supplied with 
fuse holders and should carry protected fuses of 
the most modern non-arcing type. Their capacity 
ranges from 240 to 1,800 amperes and over, the 
fuses 60 to 450 amperes apiece. Where blank 
panels are supplied, either empty sections are to be 
filled out or a special purpose is held in view. 

The so-called direct current lighting and power 
switchboards, described fully in the bulletin sheets 
of the leading electrical manufacturers, are gener- 
ally limited to a pressure of 750 volts. The switch- 
board is built up by assembling the various panels 
and connecting together by means of flat bars of 
aluminum, copper or standard sized wires. The 
bus bars are supplied specially and provision is 
made in the panels for their attachment. The 



AND SWITCHBOARDS 197 

cheapness and convenience of this style of sectional 
switchboard has recommended it strongly to the 
attention of contractors and prospective proprietors 
of private plants. 

Switchboards for Electrolytic Work. Genera- 
tors developing heavy currents for electrolytic 
work were left out of the list on account of the 
infrequency with which the design of a switch- 
board for that purpose arises. In a switchboard 
installed for this class of work switches were de- 
signed to carry 6,000 amperes apiece. In this case 
the switches can be single-poled because of the low 
pressure. Wherever connections are made the 
greatest care is necessary to secure a low resistance 
joint. Heavy copper bars are employed to con- 
duct the current from point to point. The back of 
the switchboard when finished was provided with 
triple copper bars, each bar slightly separated from 
its neighbor to give radiation whenever the current 
was conducted from point to point. Great copper 
refining and plating plants are equipped with 
switchboards of this character. 



198 ELECTRIC-WIRING, DIAGRAMS 



CHAPTER XI 

PANEL SWITCHBOARDS. STREET RAILWAY SWITCHBOARDS. 
CONNECTIONS OF COMPOUND WOUND GENERATORS IN 
A POWER HOUSE TO SWITCHBOARD AND INSTRUMENTS. 
LIGHTNING ARRESTERS. THE PANELS AND THEIR FUNC- 
TIONS. STATION FIRES THROUGH LIGHTNING. THE 
GENERATING, FEEDING AND METERING SECTIONS. 

Panel Switchboards. The panels composing the 
essential parts of a switchboard, such as the gener- 
ator panel, load panel and feeder panel, call for the 
further classification of switchboards with reference 
to these facts. 

In street railway service particularly the two 
great divisions of apparatus and parts of the 
switchboard are the generating section and the 
feeding section. Dividing the switchboard up into 
panels is convenient in a practical sense and very 
instructive from a technical standpoint. All the 
apparatus relating to the generator, covering the 
instruments previously named, are placed on one 
panel, as shown in the sketch (Fig. 73). When 
large switchboards are erected, the generator panels 
are placed on the right hand side, the feeder panels 
on the left. 

It is customary to place the load panels between 
the two. The illustrations readily convey this 



AND SWITCHBOARDS 



199 



idea, showing generator, feeder and load panels 
with the equipment supplied by the largest manu- 
facturers of electric light and power apparatus in 



VOLTMETER 



VOLTMETER VOLTMETER VOLTMETER 



CIRCUIT BREAKER 



VOLTMETER SWITCHES 



,000, 



FIG. 73. Front View of Generator Switchboard. 

the United States. The generator panels may be 
supplied with either one double-pole or two single- 
pole switches for the following reasons : If a double- 
pole switch is employed a current capacity of not 



200 ELECTRIC-WIRING, DIAGRAMS 

more than 600 amperes is allowable with this spe- 
cial design. When two single-pole switches are 
supplied the panel is constructed to have a current 
capacity of from 800 to 2,000 amperes. 

The ammeters on these panels are all made of 
a greater capacity than the panel as a whole. The 
possibility of a continued overload calls for the 
employment of ammeters reading as high as 50 
per cent, above the rated capacity of the panel. 



CIRCUIT BREAKER 




S. P SWITCHES 







FIG. 74. Front View of Feeder Switchboard. 

Where the generator panel has a double-pole switch 
mounted on it a double-pole circuit breaker is also 
employed. The load panel carries an ammeter 
and a voltmeter. This voltmeter is used to give 
the bus bar reading ordinarily or it is indispensable 
where another generator is to be put in multiple. 



AND SWITCHBOARDS 



2OI 



In this case it acts differentially, giving the differ- 
ence between the pressure of the generator and the 
bus bars, as previously described. A recording 
wattmeter giving the total external consumption 



CIRCUIT BREAKERS 




I 










FIG. 75. Feeder Panel 
(Front). 



FIG. 76. Feeder Panel 
(Back). 



of amperes or watt hours is also connected below 
in many cases. The feeder panel (Fig. 74), with its 
single-pole switches and ammeters, circuit break- 
ers and lightning arresters (frequently mounted on 
the back), represents the distributing department 



202 ELECTRIC-WIRING, DIAGRAMS 



of a large switchboard. In street railway service 
this system of designing and connecting switch- 
boards has proved a matter of incalculable value. 
The front and back view of a feeder panel is shown 



VOLTMETER 
CIRCUIT BREAKER 



S. P.S'WITCHES 



O ooo o 0o o 



RHEOSTATS 



AMMETER VOLTMETER 

\ ( \ ( 

CIRCUIT BREAKER 



DIP. VOLTMETER 



WATTMETER 



FIG. 77. Generator FIG. 78. Generator FIG. 79. Load Panel. 
Panel (Two Circuit). Panel (One Circuit). 

(Figs. 75 and 76), with the lightning arresters in 
place. The appearance of a panel switchboard 
(Fig. 80) consisting of two generator panels (Figs. 
77 and 78), one load panel (Fig. 79) and three 
feeder panels is shown, carrying out the idea of 



AND SWITCHBOARDS 



203 







S}^= 





204 ELECTRIC-WIRING, DIAGRAMS 

placing the generator panels to the right, the feeder 
panels to the left, and the load panel (Fig. 80) be- 
tween. 

Street Railway Switchboard. The ideas carried 
out by the preceding series of principles relating to 
switchboards are embodied in the illustration (Fig. 
81) showing the connections of three compound 
wound generators operating in multiple to feed 
a street railway system. The front view of the 
switchboard really represents two switchboards, 
which might be called the primary or generator 
board in compliance with the last proposition relat- 
ing to this classification ; the other, the secondary 
switchboard, would necessarily be called the dis- 
tributing or feeder board. In many stations the 
upper one is mounted on a platform above the first 
with a passage way for the attendant. 

A new feature to the reader is the upper line of 
lightning arresters protecting the outgoing feeders. 
The entire wiring plan of this switchboard is laid 
out from the generators to the generator board and 
then to the distributing section. It is a well-known 
fact that in street railway service the trolley line 
is reinforced during its entire length at regular 
intervals by connection with a system of feeders. 
By this means the pressure is kept at its normal 
value along the route and the speed of the cars 
preserved. Both track and trolley line are de- 
pendent upon this feeding system, which does not 
materially differ from that employed for incandes- 
cent lighting. The apparent complexity of the 



AND SWITCHBOARDS 



205 



switchboard is entirely due to the multiplicity of 
circuits. The key to the situation is a careful study 
of the fundamental principles underlying the theory 



. GROUND WIRE 




FIG. 81. Back View of Generator and Feeder Switchboard, Showing Dynamos 

in Multiple. 



206 ELECTRIC-WIRING, DIAGRAMS 

and construction of switchboards. In street rail- 
way service particularly the conditions of " drop " 
and " leakage " require constant study and atten- 
tion. The switchboard, as far as the generators' 
and feeders' sections are concerned, is no more than 
a means of sending out a uniform potential all over 
the system. In this respect a street railway system 
is resolved down to a wiring proposition, with 
many feeders and necessarily many centers of dis- 
tribution. 

General Principles of Switchboard Construction. 
The design of a switchboard, to be conducted 
intelligently, must cover the ground indicated not 
only by these and other sketches, but, in particular, 
the general idea that all designs must represent. 
These facts, as relating to that idea, are crystallized 
in the synopsis conveniently arranged for future 
reference found at the end of this chapter. 

Whether a switchboard be designed for direct 
or alternating current it would be wise to consult 
some such plan as the above before proceeding to 
lay out the apparatus and circuits. For switch- 
boards for incandescent lighting and street railway 
service a departure could not be made from the 
system indicated. 

Lightning Arresters. Lightning arresters are 
employed for the protection of alternating as well 
as direct current circuits.- The injury electric light 
and power circuits are exposed to under certain 
conditions are, first, short circuits ; second, grounds. 

By means of the lightning arrester protection 



AND SWITCHBOARDS 207 

against either of these breakdowns through light- 
ning discharges is afforded. The lightning arrester 
(Fig. 82) offers protection against a sudden rise 




FIG. 82. Principle of the Lightning Arrester. 

of potential in the lines by the use of, first, an air 
gap ; second, a dead ground. 

In well constructed lightning arresters the air 
gap can be so adjusted that a rise of voltage be- 
yond a certain anticipated value will bring about 
a discharge. The danger arising in lightning ar- 
resters is due to the possibility of arcing. This 
will, in many instances, take place after an enor- 
mous burst of potential, which, leaping the gap 
leading to the earth, provides a gaseous path for 
the current of the generator unless the insulation 
is perfect. When lightning strikes a station un- 
provided with adequate protection it may leap be- 
tween wires of opposite polarity, which wires, if 
near enough, will develop an arc. In several 



208 ELECTRIC-WIRING, DIAGRAMS 

notable instances it was believed that lightning 
supplied the flame and the fire to destroy the sta- 
tion. A little consideration of the direct possibil- 
ity of a high pressure discharge causing an arc 
will readily account for the destruction of prop- 
erty which ensues. In such cases the station sup- 
plies the power with which to burn itself down. 
The line is therefore provided with a pressure 
vent whenever danger may arise through exposure 
to discharges of this character. This is merely an 
air gap leading to the earth. Where a lightning 
discharge possesses a very high frequency it is 
well known theoretically and practically that the 
apparent resistance of a copper wire becomes so 
great that an air gap is preferable. On some such 
lines as this lightning arresters are designed for 
the protection of light and power circuits. 



TABLE 

PRINCIPLE OF SWITCHBOARD CONSTRUCTION FOR SHUNT AND COM- 
POUND WOUND DYNAMOS. 



Generating section. 


Metering section. 


Feeding section. 


Switches. 


Differential volt- 


Switches. 


Circuit breakers. 


meter. 


Circuit breakers. 


Bus bars. 


Ammeters. 


Bus bars. 


Ammeters. 


Wattmeter. 


Ammeters. 


Voltmeters. 




Lightning 


Rheostat. 




arresters. 



AND SWITCHBOARDS 209 



CHAPTER XII 

TESTING. THE GROUND DETECTOR. TESTING WITH A 
VOLTMETER. USE OF THE MAGNETO FOR TESTING 
INSULATION. LOCATING GROUNDED CIRCUITS. DAMP 
BASEMENTS. USE OF INSULATORS. WEATHERPROOF 
WIRE. CABLES. ROTARY CONVERTERS. THE APPLI- 
CATIONS OF ROTARY CONVERTERS. EFFICIENCY OF 
CONVERTERS. 

Testing. Faults develop in electric light circuits 
and must be discovered and removed. The most 
flagrant sources of trouble are short circuits and 
grounds. 

Short circuits are caused by the crossing or 
touching of wires. Grounds caused by wires in 
contact with gas pipes are what is generally called 
a good earth connection. Breaks in the wires are 
evident when the lamps will not burn. Short cir- 
cuits or crossed wires cause the fuses to blow. 
Poor connections in the wires occurring where 
soldering between ends has taken place is due to 
the resistance of the joint. High resistance fre- 
quently is found where wires are held under screws 
and washers, as in cutouts, switches, sockets, etc. 

Operation of the Ground Detector. For detect- 
ing heavy grounds, ground detectors are mounted 
on the switchboard. The ground detector for a 



210 ELECTRIC-WIRING, DIAGRAMS 

two-wire and three-wire system operate according 
to the following principle : Two lamps are con- 
nected in series across the two main wires. The 
connecting wire between the two lamps is grounded 
by running a wire from a gas or water pipe and 
soldering it to this connecting wire. Under ordi- 



o-f 




GROUND TO PIPE 



FIG. 83. Ground Detector for Two-wire System. 

nary circumstances when both wires are free from 
grounds the lamps burn with equal brightness. 
If the ground is on one leg of the circuit the lamp 
connected to the other leg burns 'more brightly, 
and vice versa. 

A switch is connected, as well as a safety fuse, 
between the earth and the two lamps. This switch 
is left open except when a test of this character 



AND SWITCHBOARDS 



211 



is conducted. The illustration (Fig. 83) shows 
the general arrangement of the ground detector 
for a two-wire system with lamps, switch and fuse 
mounted. 




FIG. 84. Ground Detector ior Three-wire System. 

In the next sketch (Fig. 84) is shown the gen- 
eral arrangement of the wires in a ground detector 
for a three-wire system. 

If by any mistake both switches are closed at 
one time a short circuit will occur, because both of 
the outer legs are thrown into communication and 



212 ELECTRIC-WIRING, DIAGRAMS 

short circuited by that means. Therefore it is nec- 
essary to be careful in testing to open and close 
only one switch at a time and after using it to leave 
it open. 

The illustration shows how the fact of a ground 
occurring on either the neutral or negative wire 
will make the lamp on either the negative or neu- 
tral wire light up brighter than its neighbor. The 
same is true of the lamps connected to the positive 
and neutral wires. If a ground occurs on the 
positive wire the lamp connected to the neutral 
wire will light up brighter than its neighbor, and 
the reverse. The danger from grounds arises 
more from the risk of fire than anything else. If 
two wires of opposite polarity of the same circuit 
are grounded the leakage is in proportion to the 
resistance of each or both grounds. 

In street railway practice the danger from 
grounds is found in the corrosion of pipes through 
electrolytic action. 

Testing with a Voltmeter. The voltmeter is 
employed in about the same manner as the lamps. 
It is connected between the earth and one leg of 
the circuit. If the other leg is grounded current 
will flow up into the voltmeter from the earth or 
from the other wire into the earth. Whichever 
wire gives a reading indicates that the other wire 
is grounded. The grounds may be roughly classi- 
fied as high resistance grounds, low resistance 
grounds and dead grounds. A high resistance 
ground runs into thousands of ohms ; a low resist- 



AND SWITCHBOARDS 213 

ance ground into hundreds of ohms and a dead 
ground means absolute contact between one wire 
and the earth through a gas or water pipe, etc. 
If the insulation is high the voltmeter will not 
read, but if medium or low the reading will be in 
proportion. 

Using the Magneto. The magneto is more fre- 
quently employed for line testing than any other 
piece of apparatus. One wire from the magneto 
is connected to a gas or water pipe and the other 
to each wire of the circuit in turn. 

If the magneto rings, a ground is present on the 
other wire. This method of testing while generally 
employed is sometimes deceptive, because perfect 
insulation may provide certain electrostatic condi- 
tions which will cause the magneto to receive a 
return static discharge from the circuit which may 
cause it to ring. As this is more an exceptional 
than a common case due consideration may be 
made for it. Magnetos for testing are so con- 
structed by means of the winding that they will 
ring through 1,000, 5,000, 10,000, 15,000, 20,000 and 
35,000 ohms. They are made to ring through 
higher resistances than this and are marked accord- 
ing to their capacity in this respect. A ground 
which can be rung through by a magneto is there- 
fore of the same resistance as the rating of the 
magneto or less. If an attempt is made to discover 
a ground in a heavily wound coil, such as the field 
coil of a dynamo by ringing a magneto through 
it, the experiment will be unsuccessful, for the 



2i 4 ELECTRIC-WIRING, DIAGRAMS 

reason that the rapid reversal of current from the 
magneto cannot penetrate the numerous turns of 
the coil. 

This is due to self-induction and will make it 
appear by the silence of the magneto as though 
no ground were present. 

This fact is of importance in testing any circuits 
connected to inductive devices for grounds. 

Locating Grounded Circuits. To locate a 
grounded circuit each branch must be tested syste- 
matically. This is accomplished by disconnecting 
each circuit from its cutout or from the panel 
board to which it is connected. ' By testing each 
one in turn the grounded circuit is sure to be 
located and then the wires may be examined to 
discover the cause. Abraded wires are often the 
cause. Defective insulation on the inside and out- 
side of the conduit is another. Moisture, corrosion 
and damp walls and plaster are a frequent cause 
of trouble. Wires touching on the parts of chan- 
deliers and fixtures must be regarded as among 
the chief causes of trouble and annoyance. The 
voltmeter is the most scientific and, therefore, the 
most accurate instrument to use for this purpose. 
Where the ground is heavy neither the voltmeter 
or magneto are required. Two lamps in series 
connected to the circuit in the following manner 
can be employed : One leg of the circuit is con- 
nected to the end wire of the two lamps and the 
other end to the earth through the medium of a 
gas or water pipe. This is repeated with the 



AND SWITCHBOARDS 215 

other leg of the circuit. The process is continued 
throughout every circuit until the fault is dis- 
covered. 

The magneto proves exceptionally valuable in 
locating breaks in a line. This is indicated by the 
magneto not ringing. Where the continuity of 
the circuit of a series arc light system is to be 
tested the two ends of the circuit are connected 
to the magneto directly and the test made. Poor 
connections at fuses will cause heating, frequently 
sufficiently high to melt the fuse. It is therefore 
best to examine the fuses before exploring the rest 
of the circuit for breaks. It is good practice to 
test for grounds every day in order to avoid trouble. 
In large hotels and apartment houses where the 
chandeliers and fixtures are continually handled 
breaks and grounds happen often enough to neces- 
sitate this requirement. 

Damp Basements. The grounds in damp places 
are naturally apt to be frequent, due to obvious 
causes. It is not always best to install a conduit 
system in this case, but a knob insulator equip- 
ment with rubber-covered wires. Sockets of in- 
sulating material must also be employed and fuse 
blocks must be protected from exposure to damp- 
ness by boxing. 

Insulators. The knob porcelain insulators and 
porcelain cleats in use for electric light wiring must 
be designed with reference to the mechanical strain 
to which they will be subjected as well as the in- 
sulating properties they are supposed to possess. 



216 ELECTRIC-WIRING, DIAGRAMS 



The glass as well as the porcelain insulators must 
be designed with reference to strength and insula- 
tion. The element of strength is secured by con- 
sulting the mechanical requirements in the way of 
proportioning the diameter, length, diameter of 
the hole or orifice to receive the wooden peg or 
screw, etc. The insulating power is obtained 
through its dependence on the nature of the mate- 
rial, the distance from the wire to the screw or pin 
and the extent of the hygroscopic power of the 
glass or porcelain. The materials employed are 






FIG. 85. Single Petti- FIG. 86. Double Pet- 
coat Insulator. ticoat Insulator. 



FIG. 87. Triple 
Petticoat Insulator. 



too well known to require repetition and their 
hygroscopic power is something unavoidable, but 
means may be taken to improve the insulating 
power of the material by the following scheme of 
construction : 

The petticoat, that is to say, the part of the in- 
sulator which acts as a hood to the pin, may be 
doubled or tripled, as shown in the sketches (Figs. 
85, 86 and 87), so as to increase the distance the 
current must travel from the wire to the pin, 



AND SWITCHBOARDS 217 

through the film of dust or moisture which is 
bound to collect on its surface according to the 
weather and age of the insulator. Very often for 
high potential circuits of over 5,000 volts oil insula- 
tors are used. In these, the edge of the insulator 
is turned up forming a channel in which oil is 
placed to increase the resistance in the path of an 
escaping current. 

Weatherproof Wire. This wire is used in places 
such as the name indicates, where the weather can 
get at it. The wire is made of a certain number 
of layers of braided cotton-covering soaked in a 
highly insulating compound. By this means insula- 
tion is obtained and protection against wet as well. 
In large cities where wires are mainly under- 
ground, in the form of lead-covered cables, differ- 
ent insulation is employed. But for electric light 
wires in the country, arc and alternating, and for 
street railway feeders, this wire is extensively em- 
ployed. 

Cables. The manufacture of cables is an elabo- 
rate process and the coverings of the wires they 
contain are varied according to the system peculiar 
to that particular phase of the art. The copper 
conductors are frequently covered with rubber 
compound which insulates the wire from the lead 
sheathing. If the pressure they carry is high the 
insulation is thicker. It generally varies from 
about | to f of an inch. In the case of other cables, 
the conductor is wrapped around with tough paper 
soaked in an insulating compound which gives it 



2i8 ELECTRIC-WIRING, DIAGRAMS 

flexibility as well. A third class of cables for 
electric light and power might be described as con- 
sisting of weatherproof wires incased in lead tub- 
ing. The woven covering of the wires in this case 
consists of a jute or cotton braiding saturated to 
excess with a black insulating compound which is 
supposed to resist moisture and not to deteriorate 
with age. It is imperative to have a lead sheath- 
ing so thick that porosity is absent, as that would 
invite moisture to enter and rapidly destroy the 
integrity of the cable. 

Rotary Converters. The development of the 
wiring system of a large central station is in many 
respects due to the introduction of a variety of 
new appliances whose use has led to economic 
changes of immense benefit to the installation as 
a whole. Among the appliances or devices to be 
thus considered the rotary converter possesses a 
leading interest. It has without doubt caused a 
change in engineering and station methods of the 
most far-reaching consequence. A rotary converter 
is a composite dynamo and motor combined in one 
machine. If continuous current is sent into it an 
alternating current can be developed of two or 
three phase and, conversely, if an alternating two 
or three-phase current is sent in a direct current 
will be generated. In other words it is a trans- 
forming device which receives an alternating and 
gives out a direct, or receives a direct and gives 
out an alternating current. In order to obtain this 
elasticity of operation a single generator frame is 



AND SWITCHBOARDS 219 

employed within which rotates an armature so 
wound that it can receive a two or three-phase 
current at one end or a direct current of from no 
to 550 volts at the other end. The large power 
stations whose object it is to transmit current for 
street railway power and lighting purposes can 
accomplish this object by the use of the rotary 
converter. In addition, all the generating units, as 
the phrase goes, can be installed under one roof 
and the power from this central station distributed 
with economy and efficiency from various points 
at which such power would be useful, called sub- 
stations. By erecting substations, whose function 
it is to transform and distribute the power, instead 
of building power stations a great element of ex- 
pense is removed and a satisfactory commercial 
solution is given to the problem of the distribution 
of power. 

Various Equipments. Many plants have been 
installed of immense proportions, in which these 
machines for transforming alternating into direct 
and direct into alternating current were the means 
of bringing about investments of millions of cap- 
ital. The Niagara Falls Power Company now gen- 
erate and deliver 50,000 hp. to the various factories 
and work shops, hotels and houses in Niagara 
Falls and adjacent cities and towns. Over 30,000 
hp. is drawn from the main power station and con- 
verted into continuous current for operating the 
street railway lines as well as for light and power 
in the cities of Buffalo and Lockport. 



220 ELECTRIC-WIRING, DIAGRAMS 

The leading power stations in Greater New York 
operate on the same general principle. In these 
main stations the process of developing the elec- 
trical energy is carried on, then the power as a 
high-tension, alternating current is sent to various 
substations in which it is transformed into a com- 
paratively low pressure direct current. Among 
the institutions to which reference is made may be 
mentioned the power plants and substations of the 
Manhattan Elevated Railway Company, the Metro- 
politan Street Railway Company and the Rapid 
Transit Company whose equipment for the tunnels 
is one of the greatest as well as one of the most 
elaborate in the annals of engineering. These de- 
velopments in electrical engineering are only pos- 
sible through the recognized efficacy of the " rota- 
ries " as they are called. 

Application of Rotaries. Under the following 
headings the most important applications of the 
rotary converter are given as cited by the bulletin 
of the Westinghouse Company. 

I. It may be supplied with alternating current 
and will deliver continuous current. 

II. It may be supplied with continuous current 
and will deliver alternating current. 

III. It may be connected to alternating cur- 
rent mains and operate as a simple synchronous 
motor. 

IV. It may be connected to continuous current 
mains and operate as a simple continuous current 
motor. 



AND SWITCHBOARDS 221 

V. It may be driven by mechanical power as a 
generator and develop alternating current. 

VI. It may be driven by mechanical power as a 
generator and deliver continuous current. 

VII. It may be driven by mechanical power as 
a generator and deliver both alternating and con- 
tinuous current at the same time. 

VIII. It may be connected to continuous current 
mains and deliver mechanical power from a pulley 
on the shaft and at the same time deliver from its 
collector rings an alternating current. 

IX. It may be connected to the alternating cur- 
rent mains and deliver mechanical power from a 
pulley on the shaft and at the same time deliver 
from its commutator a continuous current. 

Although generally employed for the purpose of 
transforming the character of the current and the 
pressure, converters can be operated in multiple 
or two of them can be connected so as to supply 
a three-wire system. 

Efficiency. On account of the high efficiency 
of the rotary converter, as high as that of a dynamo 
or motor of equal size, the electric light and power 
problem has been, to a large extent, solved. The 
regulation and sparking are about the same as 
would be found in an ordinary generator of equally 
good design. The Edison Company of New York, 
whose original plant was entirely composed of no 
volt dynamos operating on the three-wire system, 
has had in use for many years rotaries, by means 
of which one station can relieve another when 



222 ELECTRIC-WIRING, DIAGRAMS 

overloaded, or can help to distribute equally the 
power from one generating center to another with- 
out the necessity arising for the erection of new 
power houses, except through the natural causes of 
greatly increased demand. 



AND SWITCHBOARDS 223 



CHAPTER XIII 

IMPORTANT FEATURES OF ALTERNATING CURRENTS TO 
CONSIDER. LOSSES IN A LINE. INDUCTANCE EX- 
PLAINED. INDUCTANCE WITH ALTERNATING CUR- 
RENTS. RESISTANCE COMPARED WITH INDUCTANCE. 
EFFECT OF RESISTANCE AND INDUCTANCE ON AN 
ALTERNATING CURRENT. EFFECT OF CAPACITY ON AN 
ALTERNATING CURRENT. 

Important Features. Alternating currents pre- 
sent a different class of "phenomena when trans- 
mitted and transformed than that form of electrical 
energy termed direct. The frequency of an alter- 
nating current, or the rate at which it moves back 
and forth in the circuit; the nature of the alternat- 
ing current wave, whether its growth is relatively 
rapid or slow ; the resistance of the circuit and the 
degree to which magnetic effects can manifest 
themselves: all of these constitute important feat- 
ures (Fig. 88) in the consideration of alternating 
currents, requiring definition and elucidation. 

Losses in a Line. Whenever electricity is trans- 
mitted from point to point, by the establishment 
of a circuit, certain losses are sustained and diffi- 
culties developed which may be classified as fol- 
lows: 

i. Losses in the line due to the current and re- 



224 ELECTRIC-WIRING, DIAGRAMS 

sistance, included under the title of C 2 R or heat 
losses ; and C X R or drop. 

2. Difficulties in the line, due to the rate at which 
the current reverses. 



HEAT OR C R LOSS 



FREQUENCY EFFECT 



SELF INDUCTION 



LEAKAGE 



CONDENSER OR CAPACITY' EFFECT 



DROP OF PRESSURE 



FIG. 88. Important Features of a Circuit Carrying Alternating 
Current. 

3. Difficulties in the line, due to the amount 
of magnetism or inductance developed along its 
length, or in certain parts of it. 

4. Waste of power, due to the deficiencies in the 
insulation employed around the wire, or on the 
insulators supported on poles. 

5. Difficulties due to the electrostatic effects in 
the line through its operation as a condenser. 

It may be stated at once that capacity or con- 
denser effects, in comparison with the effects of 
self-induction, produce opposite results. Thus, 
capacity encourages the free flow of current, while 



AND SWITCHBOARDS 225 

inductance retards it. Neither the capacity or 
electrostatic effects, or the inductive effects are 
wasteful as far as the dissipation of energy is con- 
cerned Resistance wastes or degrades electrical 
energy, but not capacity or inductance. Resistance 
in a circuit develops heat if the current can operate 
conjointly with the pressure. When the current 
and pressure do not operate simultaneously, it is 
due to the effect either of self-induction or capacity. 
Inductance. The rapid reversal of the current in 
any electric circuit means the rapid reversal of the 
lines of force with which every circuit carrying a 
current is surrounded. No change can occur in the 
value of the current in a circuit without producing 
a proportionate change in the lines of force sur- 
rounding it. The mere fact that lines of force 
embrace a circuit, or, after embracing it, either in- 
crease or diminish in number, due to the increase 
or reduction of the current, means the development 
of an electromotive force, either instantaneously 
and then ceasing; or, due to a series of changes in 
the current value, lead to continued and corre- 
sponding electromotive forces through the said 
changes of current. In other words, the interlink- 
ing of magnetic lines of force with a circuit, which 
is inevitable when the current enters or leaves, 
causes an effect to be produced in the circuit called 
self-induction. It is an electromotive force (Fig. 
89) that opposes any increase of current in a cir- 
cuit, even when it first enters ; and it likewise op- 
poses a discontinuation of the current when it is 



226 ELECTRIC-WIRING, DIAGRAMS 

diminished or cut off. In the first instance, the 
current cannot enter at once at its full value ; in the 
second instance, it cannot leave at once, but tends 
to continue flowing for a short period of time. 

DIRECTION OF DIRECTION OF 



E. M. F. OF SELF E. M. F. OF 

INDUCTION ENTERING CURRENT 



DIRECTION OF E.M.F. OF DIRECTION OF E. M. F. OF 



SELF INDUCTION WHEN 
CIRCUIT IS BROKEN 


CURRENT WHEN CEASING 



FlG. 89. Opposing and Similar E M F of Self-induction Where 
Current is Made and Broken. 

An Alternating Current and Inductance. These 
few words about inductance have a very important 
bearing upon a circuit carrying an alternating cur- 
rent. An alternating current not only alternates, 
that is, reverses in direction a certain number of 
times a second, but it consists of a number of waves 
following fast after each other, each wave moving 
in an opposite direction to that preceding or suc- 
ceeding 'it. At any given instant only one wave is 



AND SWITCHBOARDS 



227 



impressed upon the line, creating a positive and 
negative polarity. But an instant after, another 
wave, whose poles are opposite to the first, per- 
meates the circuit. Thus it is evident that each 
wave represents a growing value of the current 
(Fig. 90) until it reaches its highest point; and then 



MAXIMUM POINT 




ZERO POINT 



FIG. 90. Curve Showing the Rise from and Fall to Zero in a Single 
Wa/e of E M F. 

a diminishing value, until it ceases to be. This zero 
point is the point at which a wave begins to grow 
reversely (Fig. 91) either in one direction or the 




MAXIMUM POINT 



FIG. 91. Curve Showing the Rise from and Fall to Zero in a Single 
Wave of E M F in the Opposite Direction. 

other. And it is during these changes, in the rise 
and fall (Fig. 92) of the electrical energy in the 
line, that inductance plays its part. It operates in 
the circuit in such a manner that the tendency of 



228 ELECTRIC-WIRING, DIAGRAMS 

the current to grow in value, as rapidly as it is pro- 
duced in the generator, is temporarily checked. 
The electromotive force, as it were, is already oper- 



MAX 





FIG. 92. Curve Showing a Complete Cycle of EMF. 

ating upon the circuit, or, as the phrase goes, is im- 
pressed upon the circuit for a definite though short 
period of time before the current flows in response 
to its influence, and in proportion to the resistance 
of the said circuit. Even when it does flow, its 





SEPARATION 



FIG. 93. Effect of Induction in Separating the Current and EMF. 

value, due to this condition of affairs, is neces- 
sarily checked (Fig. 93) the more the more rapidly 
the waves act upon and leave the line. In other 
words, the faster the waves move back and forth, 
the greater the effects of inductance. 



AND SWITCHBOARDS 229 

Inductance as Compared with Resistance. The 

ohmic resistance of a line is distinguished from that 
resistance due to inductance by naming one resist- 
ance and the other reactance. It is perfectly evident 
that a conducting line made of copper can become 
deficient in conducting properties if it is exposed 
to the influence of so rapid a series of alternations 
that the reactance actually prevents more than a 
small percentage of the energy to pass. The resist- 
ance, therefore, is only one of the elements in a 
line, limiting the free flow of electricity. The addi- 
tional effects of the rapid reversals of current and 
the inductance or capacity must be considered in 
conjunction with the resistance. In a line em- 
braced by a given number of lines of force, the false 
resistance will naturally increase the more rapidly 
the current in each individual wave increases or 
diminishes. But the current in each wave or half 
alternation can only vary in value quickly if the 
wave itself is passing back and forth quickly. 
From this standpoint the greater the number of 
waves per second in any circuit the more rapidly 
the current rises to its maximum from zero, and the 
more rapidly it falls back to that point. Thus the 
frequency with which an alternating current passes 
back and forth is one of the fundamental reasons 
why the combined effects of resistance, inductance 
capacity, and this said frequency, produce more re- 
active effects. The more slowly the waves travel 
back and forth, the less is this influence a para- 
mount one. The name given to this combination 



2 3 o ELECTRIC-WIRING, DIAGRAMS 

of influences is impedance. It is a value which 
takes the place of ohmic resistance alone in cal- 
culations of current in circuits traversed by alter- 
nating waves of electrical energy. 

Effect of Resistance on an Alternating Current. 
It may be distinctly stated that ohmic resistance 
has the same effect upon an alternating current as 
that experienced by a direct current. It reduces it 
in each case, as pointed out by Ohm's Law. Al- 
though other secondary effects take place, they are 
distinct from those arising due to the length of 
the copper wire, its cross section in circular mils 
and its temperature. 

Effect of Inductance on an Alternating Current. 
Another fact to be known is that inductance has 
the effect of retarding the flow of current entering 
a line. Its action is such that the electromotive 
force tending to send a current through the cir- 
cuit is effectively opposed. This develops a con- 
dition similar to that existing through a higher 
ohmic resistance in the line. For this reason it 
is termed the reactance of inductance or induction 
reactance, and can be expressed in its equivalent 
in ohms. Inductance does not dissipate energy 
as ohmic resistance, but it affects the impressed 
EMF. It is a secondary pressure, due entirely to 
changes taking place in the current. It acts to 
reduce the effectiveness of a current wave as far 
as the EMF. of said wave is concerned. It will act 
in this manner when the current is rising from 
zero to its maximum value. As each complete 



AND SWITCHBOARDS 231 

alternation consists of two waves it is evident 
that, although one sweeps through the circuit in 
an opposite direction to the other, there is a zero 
point to each from which the current rises to its 
greatest strength. During this growth of the cur- 
rent, inductance is operating against the impressed 
EMF. The lines of force of the current have created 
it as an evidence of a change of current strength. 
This change is most emphasized when the current 
passes the zero mark. At this point it is not only 
diminishing until it disappears, but it reverses and 
grows in an opposite direction. The impressed 
EMF., therefore, cannot deliver a current propor- 
tional to itself at once. An interval elapses before 
the current wave it is to pass through the circuit 
follows after it. This is called the lag of the cur- 
rent. It naturally becomes more emphasized as the 
inductance becomes more manifest. 

Effect of Capacity on an Alternating Current. 
In a circuit with capacity the current leads. The 
EMF. in this case follows after the current. In the 
case of inductance the current follows after the 
pressure. Instead of a weak and increasing cur- 
rent, as with inductance, there is a strong and 
diminishing current with capacity. The lag of 
the current behind the EMF. in the case of induc- 
tance in the circuit, is replaced by a lag of the EMF. 
after the current, in the case of capacity in the cir- 
cuit. In this case the current has " lead " instead 
of lag. Both inductance and capacity affect the 
value of the current, and the difference of phase 



23'a ELECTRIC-WIRING, DIAGRAMS 

between the EMF. and current. Inductance affects 
the circuit, with an entering- current, as though 
a greater resistance were present ; capacity affects 
a circuit with an entering current as though a 
lesser resistance were present. Capacity therefore 
produces the effect of less resistance, but not less 
than the ohmic resistance itself. The value of ca- 
pacity in connection with inductance, is its effect 
in reducing the inductance. In other words, in- 
ductance and capacity are the antithesis of each 
other in circuits traversed by alternating currents. 
When present in a certain relationship one de,- 
stroys the effects of the other. 



AND SWITCHBOARDS 233 



CHAPTER XIV 

CALCULATION OF REACTANCE. VALUE OF INDUCTION RE- 
ACTANCE. VALUE OF CAPACITY REACTANCE. CALCU- 
LATION OF IMPEDANCE IN A CIRCUIT. THE UNIT OF 
SELF INDUCTION. THE POWER FACTOR. 

Calculation of Reactance. The calculation of the 
two reactances, due to self induction and capacity 
in the circuit, is given in terms of the frequency 
and henries of inductance for the induction react- 
ance; and in terms of the frequency and capacity 
in farads for the capacity reactance. Both may 
be given numerical values which can be used in 
obtaining results for circuits through which an 
alternating current passes, conforming in the char- 
acter of its waves to those falling within the scope 
of the formulas. 

Value of Induction Reactance. Although the 
frequency of an alternating current may be given 
in reversals or waves per second, the calculation 
of the induction reactance calls for the multiplica- 
tion of this value by a quantity equal to 2. TT or 2 X 
3.1416 equal to 6.2832. The result of this will be as 
follows : 

Where f = frequency or complete alternations per second, 

TT = 3.1416, 

L = inductance in henries of circuit, 

then the reactance due to the self induction and frequency 
will bc2X7rXfXL = 6.2832 X f X L. 



234 ELECTRIC-WIRING, DIAGRAMS 

Example. If the inductive reactance is to be 
calculated for a circuit, having a self induction of 
5 henries, through which an alternating current 
passes of a frequency of 125 per second, then the 
reactance = 6.2832 X 125 X 5 = 3927. 

This value represents the equivalent of an equal 
number of ohms with an increasing current in the 
circuit, but it will not dissipate nor degrade energy 
during its development in the said circuit. 

Value of Capacity Reactance. Reactance caused 
by capacity is calculated in terms of the frequency 
and farads. The value of the reactance is given 
by the formula : 

Capacity reactance = i-v-2X7rXfXK 
where IT = 3.1416 

f = frequency of alternations 
K = capacity in farads 

this gives a value of . to the reactance. 



If a circuit has a capacity of y^ of a farad and 
the frequency is equal to 125 cycles a second, then 
the reactance will be : 



6.283* X 1*5 X,^ ' -' 

In the application of this formula it is evident 
that the lower the value of the capacity the greater 
the reactance. For instance, if K = y^Vo instead 
of YJ-y, then the reactance becomes greater, or 1.27. 
In other words, the greater the capacity of the 
condenser, or the greater the electrostatic capacity 
of the line, the less the reactance. But the less 



AND SWITCHBOARDS 235 

the capacity, the greater the reactance. In fact, 
with a very small capacity, the reactance would be 
practically as great as though only inductance was 
present. If the capacity in a circuit = 10 micro- 
farads, or TTnroWo- of a farad, and the frequency 
is 120 per second, then on the same terms the 
reactance would be equal to i -=- 6.2832 X 120 X 
.000010, which is equal to I -:~ .00754= 132.6. In 
calculations of capacity reactance, the capacity 
must not be used in the formula as anything else 
than a fractional or decimal part of a farad. Micro- 
farads cannot be used as units but only as so many 
millionths of a farad. 

Calculation of Impedance in a Circuit. The con- 
ditions developed in a circuit carrying an alternat- 
ing current are due to three distinct influences. 
These influences are combined together in produc- 
ing an impedance to the free flow of current. They 
consist of, first, the well known effects of ohmic 
resistance ; second, the reactance due to inductance ; 
and third, the reactance due to capacity. 

If the three are combined in the form of a simple 
formula the following is obtained: 

Impedance = 
\/ohms 2 -|- (Inductive reactance capacity reactance) 2 . 

The result obtained by calculation is what has 
been called spurious or false resistance, but it is 
merely the ohmic resistance and reactance acting 
conjointly. If, for instance, the resistance of a 
circuit = 10 ohms, the induction reactance = 50, 



236 ELECTRIC-WIRING, DIAGRAMS 

and the capacity reactance = 30, then the result 
would be as follows : 

Impedance = 

V 10 X 10 + (50 3o) 2 ~~ -y/ ioo + 400 ~ -\/ 500 
or 22.3. 

In other words, although the circuit has only 10 
ohms resistance due to the wire itself, the react- 
ances build its apparent resistance up to 22.3. If 
the capacity reactance was so low as to be neg- 
ligible in this case, the impedance would become 
^/ ioo + 2500, or about 51. It is readily seen that 
if the ohmic resistance of a circuit or line is very 
low, then the reactance is all the resistance ex- 
perienced by the current. For instance, if the 
resistance is only 5 ohms, then the square of 5 
compared with the square of 50 becomes less im- 
portant. If the line resistance is only I ohm, then 
-V/ 1 + 2 5 i s practically the square root of the 
reactance squared. In other words, when low re- 
sistance and high inductance exist, the resistance may 
be neglected. 

The Unit of Self Induction, the Henry. Defini- 
tions of various kinds are given to express the 
meaning of the henry or unit of self induction. 
Though primarily caused by the development of 
lines of force around a circuit, either when the 
current is increasing or diminishing, a specific 
effect must be produced to entitle the circuit to that 
qualification. The circuit must be so constituted 



AND SWITCHBOARDS 237 

that if the current increases or diminishes one am- 
pere in a second an electromotive force of I volt 
is thereby produced. By this is meant that the 
number of turns of wire, or at least the length of 
the wire, will be embraced, interlinked, or cut by 
a certain number of lines of force in a second. 
These lines of force, developed in the course of a 
second by the current changing to the extent of 
i ampere, will operate upon the circuit, producing 
a degree of inductance called i henry and repre- 
sented by the letter L. In a circuit carrying an 
alternating current, the current and pressure wave 
consists of a start from zero, a rise to a maximum, 
and a fall to zero. During the rise from zero self 
induction is in opposition to the impressed EMF. 
Also, during the fall from its maximum value to 
zero, the self induction tends to prevent the re- 
duction of EMF. The case thus presents itself of 
an opposition to the impressed EMF. during the rise 
from zero, twice during each complete cycle ; also 
the tendency of the self inductive effect to prevent 
the impressed EMF. reaching zero, twice during 
each complete cycle. Dividing a cycle up into four 
quarters of 90 degrees apiece, the first and third 
quadrants show a back pressure to the impressed 
EMF., the second and fourth quadrants show a for- 
ward inductive pressure with the impressed EMF. 
It is quite evident that this phenomenon will cause 
so great a gap, as it were, between the impressed 
EMF. and current, if much inductance is present, 
that in wiring circuits and power lines the degree 



238 ELECTRIC-WIRING, DIAGRAMS 

to which this affects the total watts must be 
known. 

The Power Factor. The degree of electrical 
separation between the EMF. and current is measured 
by an angle. This angle represents a short period of 
time, also an angle with respect to the entire cycle 
of 360. If it equals 90, the circuit is not carrying 
a useful current. Each quadrant is 90 (see Fig. 
94) ; each half cycle 180 ; and the whole cycle 360. 




180' 



270 




Flo. 94. The 360 Representing a Complete Cycle. 

The pressure noted in a voltmeter or the current 
noted in an ammeter is not the highest value of 
either. As the lowest is zero, it is evident that the 
average or mean value must be between the two. 
The wattmeter, therefore, records the power pass- 
ing through it, not the product of the maximum 
value of the volts and amperes of the alternations, 
but the effective values. In direct current work, 
multiplying amperes by volts gives watts at once. 
In alternating current work, multiplying volts by 



AND SWITCHBOARDS 



239 



amperes is not enough, even though their effective 
values may be found. The EMF. and current may 
not appear simultaneously in the circuit. They 
may differ in phase from each other by an angle 
called < (Phi) (see Fig. 95). If the two elements 




ANGLE OF SEPARATION 
DUE TO LAO 




FIG. 95. Lag of Current Behind EMF. 

of power are separated from each other by quite 
an interval of time, then < is a large angle. If the 
time is very short, < is small. The reason why <f> 
is considered at all is because it expresses the de- 
gree to which the volts and amperes of the circuit 
cooperate. It is a measure, in a way, of the amount 
of inductance present. 

A Wattless Current. In an non-inductive cir- 
cuit there is no </> ; in a circuit with much induction, 
in fact too much, < will indicate so great a lack of 
cooperation between E and C, that no power will 
be available, even though a high pressure and a 
large current are noted on separate meters. This is 
a case of a -wattless current, and a comparison made 
between the true power and the apparent power 
would be readily discerned by means of what is 
called the cosine of <, or the power factor. When 



2 4 o ELECTRIC-WIRING, DIAGRAMS 

the EMF. impressed upon the line and the current 
are so related through the absence of inductance or 
capacity that they operate simultaneously, then the 
cos. $ = 1, or the power factor is at its highest 
value. If inductance is developed in the line, the 
cos. < is less than i ; in fact, as the inductance is 
increased the value of cos. </> diminishes toward 
zero. 

This is simply a diagrammatic way of repre- 
senting the manner in which the lack of coopera- 
tion of E and C is made apparent. The less they 
cooperate, or the greater the lag, the more nearly 
the angle < approaches 90. In utilizing the power 
factor, the volts and amperes are multiplied to- 
gether and by the cos. <. 




.0=90 
COS (J) = 



FIG. 96. A Wattless Current where the EMF. and Current Are 90 
Apart, through Induction. 

For instance, if the angle of lag is o, then cos. 
< == i, and EXCXi = EXC. But if the angle 
of lag = 90 (Fig. 96), then cos. </> ==o and E X C 
X o = o, or there is no power. Between these two 
limits of zero and i, the power factor will vary for 



AND SWITCHBOARDS 



241 



every circuit carrying an alternating current. If 
the power factor of a circuit is not known, and 
there is pronounced inductance present, the exact 
value of the power is problematic. In circuits sup- 
plying current for light or power the presence of 
machinery or apparatus containing inductance may 
diminish the available amount of power. In the 
following table the value of the cosine is given 
corresponding to the angular values of o to 90: 

VALUE OF THE COSINE OF <f> FROM o TO 90. 



en 




en 




en 




en 




en 








I 




g 




1 








<u 

4J 









$ 





ff 


a; 




j 


1 


o 


If 


V 


be 

_o 


u 


w 


C 


T3 


c 


*"U 


c 


'O 


C 


*"O 


c 


*o 


c 


c 


'o 


C 


8 


c 


'1 


s 


' 


e 


"s 


c 


' 





U 


O 


u 


V 


U 


<D 


U 


o> 


u 


jy 


U 


tc 




"bb 




"bb 




*bb 




"bb 




bC 




C 




c 




c 




c 




c 




C 







I.OOO 


16 


.961 


32 


.848 47 


.682 


62 


.469 


77 


.225 


I 


999 


i7 


956 


33 


.838 


48 


.669 


63 


454 


78 


.208 


2 


999 


18 


.951 


34 


.829 


49 


.656 


64 


438 


79 


.191 


3 


998 


19 


945 


35 


.819 


5 


643 


65 


.422 


80 


.174 


4 


997 


20 


.940 


36 


.809 


51 


.629 


66 


.407 


81 


.156 


5 


.996 


21 


934 


37 


798 


52 


.6l6 


67 


.391 


82 


139 


6 


995 


22 


.927 


38 


.788 


53 


.602 


68 


374 


83 


.122 


7 


992 


2 3 


.920 


39 


777 


54 


.588 


69 


358 


84 


.105 


8 


.990 


24 


.913 


40 


.766 


55 


574 


70 


342 


85 


.087 


9 


.988 


25 


.906 


41 


754 


56 


559 


7 1 


326 


86 


.O7O 


10 


985 


26 


899 


42 


743 


57 


545 


72 


309 


87 


.052 


ii 


.982 


27 


.891 


43 


73 1 


58 


530 


73 


.292 


88 


035 


12 


.978 


28 


.883 


44 


.719 


59 


.515 


74 


.276 


89 


.017 


13 


974 


29 


875 


45 


.707 


60 


.500 


75 


259 


90 


.000 


14 


.970 


30 


.866 


46 


695 


61 


.484 


76 


.242 






15 


.966 


3 1 


857 



















242 ELECTRIC-WIRING, DIAGRAMS 



CHAPTER XV 

CIRCULAR MILS FOR ALTERNATING CURRENT MAINS. VALUE 
OF C FOR SINGLE PHASE CURRENTS. CIRCULAR MILS 
CALCULATED FOR SINGLE PHASE CIRCUITS. CIRCULAR 
MILS CALCULATED FOR TWO PHASE CIRCUITS. CIRCU- 
LAR MILS CALCULATED FOR THREE PHASE CIRCUITS. 
AVERAGE POWER FACTORS. WEIGHT OF COPPER. THE 
INDUCTION MOTOR. SYNCHRONOUS MOTORS. ROTARIES 
IN POWER TRANSMISSION. ROTARIES IN ELECTRIC 
LIGHT STATIONS. TWO AND THREE PHASE ALTERNA- 
TOR CONNECTIONS. 

Size of Wire in Circular Mils for Alternating 
Current Mains. The size of a conductor carrying 
an alternating current is calculated with reference 
to the power factor by the following formula : 

Circular mils = DxWXC-^pXE 2 , 
in which W = watts delivered, 
D = length of run, 

p = loss in line in per cent, of power delivered, 
E = volts between receiving end of circuit, 
C = 2,160 for direct current, 

but varies according to the following, for single 
phase, two phase and three phase currents : 

Value of C for single phase currents with power 
factors of the values given as follows : 

Power factors 100 95 90 85 80 

Value of C 2,160 2,400 2,660 3,000 3,380 



AND SWITCHBOARDS 243 

Example. To find the current and circular mils 
required for a circuit delivering 10,000 watts, at a 
pressure of 100 volts, of a run of 1,000 feet. 

Current = W X T -=- E where 
T = 1.25 for single phase, 
= .62 " two 
= .72 " three " with a power factor of 80. 

For single phase, therefore, calling this power 
factor 80 : 

Current = 10,000 X 1.25 -T- 100 
= 12.500 -r- 100 
= 125 amperes. 

Circular Mils with Single Phase. Circular mils 
for single phase are then calculated by the formula 
in which they are equal to D X W X C -f- p X E 2 
where 

D = 1,000 ft. = length of run, 

W= 10,000= watts delivered, 

C = 3,380 = constant employed with a power factor of So, 

p = 10 per cent. = loss in line in per cent, of power 
delivered. 

E 2 = E X E = 100 X 100 = 10,000 = pressure at the 
receiving end squared. 

D X W X C -f- p X E 2 = 1,000 X 10,000 X 3,380 -=- 10 X 

10,000, 33,800,000,000 

- = 338,000 circu- 
100,000 

lar mils, with 10 per cent, drop, representing a wire equal 
to a No. oooooo B. & S. 

The above calculations for a single phase system 
of wiring can be applied to the finding of the cir- 
cular mils required for either a feeder, main, or 



244 ELECTRIC-WIRING, DIAGRAMS 

branch. In each case the constant C must be 
adopted according to the power factor of the cir- 
cuit. If, in the last case, the power factor was 90 
instead of 80, the constant would have been 2,660 
instead of 3,380. The circular mils would have 
been as follows : 

. , ., 1,000 X 10,000 X 2,660 
Circular mils = - - = 266,000, 

100,000 

instead of 338,000. The difference between the two 
results is due to the difference in the power factors 
of the hypothetical circuits respectively. 

Circular Mils with Two Phase. The value of 
the current in a two phase circuit may be found by 
the formula W X T -f- E, where 

T = .62 for two phase circuits with power factor of 80, 

W= watts delivered, 

E = volts between the receiving ends of the circuit. 

If, for instance, 10,000 watts are to be delivered 
at a pressure of 100 volts over a run of 1,000 feet, 
then the current in any leg of the circuit would be 
10,000 X -62 -7- 100 = 6200 -r- 100 = 62 amperes. 

Values of T with Different Power Factors. For 
calculating the current in circuits of single, two 
and three phase circuits the following table, giving 
the values of T, will prove very useful with different 
power factors. It will be noted, that the variable value 
of T for the different cases specified, increases as the 
power factor diminishes. 



AND SWITCHBOARDS 



245 





Power factors. 


100 


95 


90 


85 


80 


Value of T for single 
phase 


I.OO 

50 
58 


1.05 

53 
.61 


i. ii 

55 
.64 


1.17 

59 
.68 


1.25 
.62 

.72 


Value of T for two 
phase (4 wire) . 


Value of T for three 
phase (3 wire) 





By means of this table the value of the current 
in a three phase circuit, as well as a one or two 
phase, may be found, with circuit conditions giving 
a power factor of from 80 to 100. 

In the case of a three phase circuit, delivering 
10,000 watts at a pressure of 100 volts, the current, 
with a power factor of 80, would equal 10,000 X -7 2 
-I- 100 = 7200 -:- 100 = 72 amperes. The constant 
.72 is taken from the table under the power factor 
80. If the power factor had been 85 or 90, etc., the 
constant corresponding would have been selected 
accordingly. 

A table by means of which the circular mils of 
any phase of current may be readily found is given 
in the following, under the title of " Values of C." 

In this, as well as in other instances, it has been 
found advisable, for the sake of simplicity, to present 
useful figures in a tabular form. The convenience of 
this method is discovered wherever arbitrary values 
are apt to be used, instead of those based upon correct 
scientific data. The values of C, it will be noted, in- 
crease with the diminishing values of the power factor. 



246 ELECTRIC-WIRING, DIAGRAMS 



TABLE. 





Power factors of circuits. 


100 


95 


90 


85 


80 


Values of C for single 
phase circuits 


2IuO 


2400 


2660 


3000 


338o 


Values of C for two 


phase circuits (4 wire) 
Values of C for three 


I080 


1200 


J 33 


1500 


1690 


phase circuits (3 wire) 


I080 


I2OO 


1330 


1500 


1690 



In this table may be found the constant which 
can be used in finding the circular mils of a two 
phase circuit by the formula : Circular mils D X 
W X C -r- p X E 2 . Taking the last case of 10,000 
watts sent 1,000 feet at a pressure of 100 volts with 
10 per cent, drop and with a power factor of 90, 
then the size of wire equals the following: 

Circular mils of two phase (four wire) circuit = 

D X W X 1,330 - P X E 2 , 
where D = 1,000 ft., 

W = 10,000 watts 

C =1,330 (see table) 

p = 10 

E 2 = 100 X TOO = 10,000. 

Circular mils = 1,000 X 10,000 X 1,330 -r- 10 X 10,000, 

= I3,3OO,OOO,OOO -7- 100,000, 

= 133,000 or a No. oo B. & S. with a 10 per 
cent. drop. 

If the power factor is 85, then the constant be- 



AND SWITCHBOARDS 247 

comes 1,500 instead of 1,330, and the resulting size 
of wire larger as shown by the calculation : 

Circ. mils = 1,000 X 10,000 X 1,500 -j- 10 X 10,000, 
or circ. mils = 15,000,000,000 -=- 100,000, 

= 150,000 or a No. ooo B. & S. gauge. 

Circular Mils with Three Phase. Calculating 
the current and circular mils for three phase cir- 
cuits is as simple with the use of constants as in 
the case of single and two phase circuits. As al- 
ready stated, the power factor of the circuit governs 
the value of the constant. Assuming a power fac- 
tor of 90, in the case of 30,000 watts, sent a distance 
of 5,000 feet at a pressure of 1,000 volts with a 10 
per cent, drop, the current and circular mils would 
be as follows: 

Current in amperes = W X T -*- E, where W = 30,000, 
T = .64 (see table giving values of T with power factor of 
90), and E = 1,000 : then 

Current in amperes = 30,000 X .64 -r- 1,000 
current in amperes == 19,200 -h 1,000 = 19.2. 

The number of circular mils required will be 
equal to 

D X W X C -^ p X E 2 , in which the following values 
are found : 

D = 5,000 ft., length of the power line, 

W = 30,000 watts delivered at the farther end, 

C = 1,330 for (3 wire, 3 phase), according to table, 

p = 10 per cent. 

E 2 = 1,000 X 1,000 = volts at receiving end squared, 



24 8 ELECTRIC-WIRING, DIAGRAMS 

therefore the circular mils = 5,000 X 30,000 X 1,330 -=- 

10 X 1,000,000, 

circular mils = 199,500,000,000 -r- 10,000,000, 
circular mils = 19,950 or a No. 7 B. & S. gauge. 

A change of power factor will bring about an- 
other result. As, for instance, a power factor of 80 
instead of 90, which makes the constant (see table) 
1,690 instead of 1,330, and gives a result as follows: 

Circular mils = 5,000 X 30,000 X 1,690 -i- 10 X 1,000,000, 
circular mils = 253,500,000,000 -j- 10,000,000, 
circular mils = 25,350 or a No. 6 B. & S. gauge. 

Average Power Factors for Circuits. The cir- 
cuits employed for lighting, power or combination 
work naturally have different power factors. 

1. For instance, in regular lighting the power 
factor will vary from 90 to 95 per cent. If syn- 
chronous motors are installed as well, the power 
factor may diminish, but it will average up between 
these figures. 

2. For electric lighting and induction motors the 
power factor will be lower, somewhere between 85 
and 90 per cent. The reason for the reduction is 
found in the inductance introduced into the circuit 
by the motors. 

3. Where only induction motors are operated on 
the circuit the power factor will fall again to a 
lower value, lying between 80 and 85 per cent. 

In calculations of the current in one, two and 
three phase circuits great care must be taken not 
to confuse the constants employed. The same care 



AND SWITCHBOARDS 249 

must be exercised in calculating the circular mils 
of similar circuits. The advantage of knowing the 
current in the conductors is found in comparing 
the respective weights of wire needed for house 
lighting or power transmission in various instances. 

Weight of Copper. After rinding the size of wire 
in circular mils, its weight is readily determined 
in pounds from the table giving circular mils, re- 
sistance, etc., in fact, from the wire table direct, 
which will supply the information in pounds per 
thousand feet. A very simple and rapid way is to 
divide the circular mils by 62.5 to get the pounds 
per mile. For instance, a mile of No. 10 B. & S. 
copper wire of 10,400 circular mils = 10,400 -=- 62.5 
= 166 pounds of copper per mile. 

The Induction Motor. This motor requires no 
exciter and will start from rest with a moderate load. 
It differs from the type called synchronous in that 
it is started on two or three phase circuits by means 
of specially constructed transformers, called auto- 
transformers (Figs. 98 and 99), which permit it to 
receive a low pressure when beginning to speed 
up. An ordinary two way switch will be sufficient 
to control the current when starting and stopping, 
in conjunction with the auto-transformers. When 
running idle, an induction motor takes only suffi- 
cient current to operate itself and supply certain 
inherent losses. 

It consists of a stationary field or stator within 
which rotates the part developing the mechanical 
power (Fig. 97) called the rotor. As the magnetic 



250 ELECTRIC-WIRING, DIAGRAMS 

field sweeps around, as it were, its influence upon 
the rotor is to pull it around as well. This is due 
to the development of induced currents in the rotor, 




FIG. 97. Elements of an Induction Motor. 

in virtue of which a reaction occurs which mani- 
fests itself as rotation, giving it in consequence 
the name of induction motor. The ratio of the 
revolutions of the rotor to the revolutions of the 
stator, that is, of the rotating magnetic field it pro- 
duces, is a measure of the efficiency. If speed of 
field = B and speed of rotor = A, then if B = i,ooo 
and A = 900, the efficiency equals 900 -f- 1,000 = 90 
per cent. 



AND SWITCHBOARDS 



251 



Rotors may be of the type called squirrel cage, 
or they may have collector rings. In both instances 
a starting resistance is supplied. This resistance 
cuts itself in and out automatically when the motor 
starts from rest. Where the rotor has collector 
rings, an external speed controlling resistance is 
employed. Wiring circuits of a two and three phase 
induction motor are shown in Figs. 98 and 99. 



AUTO TRANSFORMER OF 1 PHASE 



2 PHASE INDUCTION 
MOTOR 



SWITCH CONNECTIONS'. DOUBLE 
THROW SWITCH 




AUTO TRANSFORMER OF 2 PHASE 

FIG. 98. Connections of a Two Phase Induction Motor, Showing 
Connections of Auto-transformers to a Starting Switch. 



A single phase induction motor requires to be 
started either by hand, by machine, or by splitting 
the single phase by special means, so that it acts 
like a two phase current temporarily, until the rotor 
is up to speed. 

Synchronous Motors. This motor must be 
started from rest, and possesses an exciter to ener- 
gize its field. It possesses collector rings and 
brushes, and cannot be brought up to speed unless 



2 5 2 ELECTRIC-WIRING, DIAGRAMS 

all load is removed. It is really a small alternator 
speeded up, when fed with current, until it gets 
into synchronism or step. If the motor is so over- 




FIG. 99. Switch Connections of a Three Phase Induction Motor 
Showing Auto-transformers in Position. 

loaded that its speed drops sufficiently for it to 
fall out of step, it will cease turning altogether. 
A drop in the voltage will cause the same result. 
An extra starting device, supplied with power from 
a foreign source, is necessary in throwing it into 
rotation. For this purpose an induction motor 
with split phase device, a gas engine, a direct cur- 
rent motor, if convenient, or a clutch receiving 
power from a line of belting, is utilized. 

Rotaries in Power Transmission. In the accom- 



AND SWITCHBOARDS 253 

panying sketch (Fig. 100) is shown the wiring 
plan of a power transmission plant with rotary 
converters in circuit performing the function for 
which they were designed, viz., the transforma- 



500 VOLT CONTINUOUS 




FIG. 100. Elements of a Power Transmission Plant. 

tion of alternating into continuous current at the 
receiving end, and the transformation of low press- 
ure alternating into high pressure alternating by 
means of alternating current transformers at the 
transmitting end. The alternating current trans- 
former consists of a magnetic circuit embracing 
two coils, a high and low pressure coil. By means 
of this device (Figs. 101 and 102) the pressure and 
amperes are converted either higher or lower, the 
total watts, with the exception of those naturally 
lost during the process, remaining the same. The 
transformers are termed step up transformers and 
step down transformers according to the purpose 
involved in their design. 

The windings of transformers are in the same 



254 ELECTRIC-WIRING, DIAGRAMS 

proportion as the electromotive forces they gen- 
erate. That is to say, if the primary winding re- 
ceives 40 volts and has 40 turns the secondary 
winding to give 8 volts must have 8 turns. This 



WINDING 5 TO 1 
PRESSURE .& TO 1 



PRESSURE 
80 VOLTS 


TURNS ON 
PRIMARY 40 ] 


% 


IH 


TURNS ON 

SECONDARY e PRESSURE 

8 VOLTS 



FIG. 101. Principle of Transformer Winding. 

gives a ratio of 5 to i, and is termed " ratio of 
transformation." 

Rotaries in Electric Light Stations. The applica- 
tion of rotaries, as previously stated, has, in a meas- 
ure, solved the problem of power distribution with 



500V. ALTERNATING 



500V. ALTERNATING 



1 


-- 
-" ' 

. 
^- 


' '. 


--^. 
"""^ 

"""-* 


'- POWER LINE ! 
n ^ 




i '^ 



STEP UP TRANSFORMER STEP DOWN TRANSFORMER 

FIG. 102. Step up and Step down Transformer in Service. 



reference to the use of sub-stations and the degree 
of assistance one large central station can give to 
other smaller stations in various parts of the city 
supplying the same circuits. The transformer and 
the rotary have been the direct means of bringing 



AND SWITCHBOARDS 



2 55 



about a revolution in lighting methods in direct 
current stations. 

In the illustration (Fig. 103) is shown the ma- 
chinery employed and way in which rotaries play 
their part in regard to the generation of direct 



110 VOLT 110 VOLT 

CURRENT DYNAMOS 




S PHASE STE" UP TRANSFORMER 
500 TO 500O.VOLTS 



I PHASE STEP DOWN TRANSFORMED 
5000 TO 500J/OLTS 



FIG. 103. Method of Distributing Power to Sub-stations as Em- 
ployed by the Edison Company. 



current and its subsequent distribution to a sub- 
station, if it represents a surplus of power or if the 
distant station is approaching a point of overload. 
In either case the system is of incalculable benefit 
as regards elasticity and economy. By adopting 
this system on a large scale the necessity for any 
other than a large central station disappears. It 
becomes the center or nucleus of a number of sub- 
stations, which distribute the electricity after re- 
ceiving it, through the medium of rotaries, to the 
outlying circuits in their vicinity. 

Two Phase Lighting System. As this system 
relates to power transmission and electric lighting 



256 ELECTRIC-WIRING, DIAGRAMS 

it must be included as a method which practice 
has shown to be of leading importance. By means 
of two or three phase currents, as already stated, 
it is possible to utilize self-starting alternating cur- 
rent motors. Formerly, all alternating current 
motors were started by some external means, such 
as an engine or a direct current motor, or a means 
was found, as previously mentioned, of developing 
in a simple alternating current, called a single phase 
current, the equivalent of two phases, by which 
an alternating current motor became self-starting. 
The two and three phase current, however, is 
generated and utilized because it may be used not 
only for electric lighting but for motors with- 
out any accessories in the way of starting devices 
making them fundamentally self-starting. The gen- 
eral plan of the connections of a two phase alter- 
nator to the four lines by which its power is trans- 
mitted, as given by the Westinghouse Company, is 
shown in the illustration (Fig. 104). The auxiliary 
field is obtained by transforming the alternating 
into direct current by means of a commutator and 
sending this current into the additional field wind- 
ing designated. 

The Three Phase System. The plan of connec- 
tions relating to this system is also shown (Fig. 
105) with auxiliary field connections as in the 
two phase system. In addition to the ordinary 
winding the auxiliary winding is employed, giving 
rise to the expression " composite winding." The 
additional coil of the series transformer receives 



AND SWITCHBOARDS 



257 



AUXILIARY FIELD 



40C 



A, B. t 



:cc 



40C 




JUUUUUL s 
1 




FIG. 104. Diagram of Connections for Two Phase 



DOT 

<-2000> 



Alternators. 

AUXILIARY FIELD 




ABC FIG. 105. Diagram of Connections for Three Phase 

Alternators. 



258 ELECTRIC-WIRING, DIAGRAMS 

a low potential current proportional to the main 
current. This current when rectified acts upon 
the field of the alternator through the auxiliary 
winding. 

It depends upon whether the main purpose is 
electric lighting with motor circuits incidental, or 
whether it is entirely a power supply for motors 
as to the wiring at the switchboard for a two 
phase system. A choice may be made of two 
methods : 

First All four-wire circuits if motors are the 
principal purpose. 

Second All three-wire circuits if lighting is the 
main object. 

In the second case the three wires, A lt Bj and 
A 2 or Bj, A 2 and B 2 are tapped. Transformers are 
connected and the pressure lowered to the point 
required. 



INDEX 



Absorption of light by globes, 164. 

Accessories of conduit, 138. 

Adjustment of arresters, 207. 

Alternating current, effect of ca- 
pacity on an, 231. 

Alternating current, effect of in- 
ductance, 230. 

Alternating current, effect of re- 
sistance, 230. 

Alternating current, line losses, 
224. 

Alternating current mains, size 
of wire for, 242. 

Alternating current waves, 229. 

Alternator connections for three- 
phase, 257. 

Alternator connections for two- 
phase, 257. 

Alternator elements, 122. 

Amperes allowed in conduit work, 
148. 

Amperes allowed in insulator 
work, 148. 

Amperes with a given insulation 
resistance, 149. 

Analysis of a ten-lamp circuit, 43. 

Analysis of a 22o-volt system, 103. 

Analysis of dro in ten-lamp cir- 
cuit, 45. 



Analysis of switchboards, 199. 

Analysis of Wiedemann system, 
47, 48. 

Angle of lag, 239. 

Apparatus of lighting circuits, 1 76 

Apparatus of switchboards, 168. 

Application of rotaries, 220. 

Application of shunt and com- 
pound wound dynamos, 84. 

Application o'f Wheatstone 
bridge, 91. 

Arc light system, 28. 

Area lit and candle power, 163. 

Arresters, lightning, 201. 

Arresters, mounted, 201. 

Armored conduit in damp places, 
136. 

Assembling a panel switchboard, 
196. 

Asphaltic paper conduit, 1 28. 

An alternating current meeting 
inductance, 226. 

Auto transformers, 249. 

Automatic dynamo, 171. 

Auxiliary field, 256. 

Average power factors, 248. 

B 

Back EMF. of motor, 115. 
Back pressure of inductance, 226. 
Balancing the bridge, 92. 



259 



260 



INDEX 



Balancing a three-wire system, 

104. 

Bends of conduit, 128. 
Bends, couplings, elbow clamps, 

133- 

Branches, feeders, mains, 66. 
Brass armored, accessories of, 

138. 

Brass armored conduit, 128. 
Bridge of lamps, 92. 



Cables, 217. 

Calculation of back EMF., 118. 

Calculation of capacity reac- 
tance, 234. 

Calculation of drop, 24. 

Calculation of impedance, 235. 

Calculation of mains, feeders, 
branches, 68. 

Calculation of power, 38. 

Calculation of resistance of wires, 

25- 

Calculation of reactance, 233. 

Calculation of a simple circuit, 42. 

Calculation of two-phase mains, 
244. 

Calculation of weight of wire, no. 

Calculation of wires for three- 
wire system, 106. 

Calculating unequal resistances in 
multiple, 35. 

Calculating a power line, 59. 

Candle power of commercial 
lamps, 1 60. 

Candle power and pressure, 161. 

Candle power per watt, 159. 



Capacity of generator panels, 

194. 

Capacity and inductance, 232. 
Capacity in a line, 224. 
Capacity reactance calculated, 

234- 

Carrying capacity of wires, 40. 
Center of distribution, 72. 
Centers of distribution, table of, 

74- 

Central station lighting, 85. 
Chandeliers, use of, 166. 
Character of glass and light, 164. 
Choosing conduit, 130. 
Choosing globes, 164. 
Circuit breaker, 170. 
Circuit breakers in power plants, 

187. 
Circuit of ten lamps, analyzed, 

43- 

Circuits tested, 209. 
Circuits, with average power 

factors, 248. 

Circular mils and drop, 31. 
Circular mils, drop and sizes, 

table of, 71. 
Circular mils and size, by wiring 

table, 53. 
Circular mils, feet of wire and 

ohms, table of, 33. 
Circular mils for two-phase, 244. 
Circular mils for three-phase, 

247. 
Circular mils for single phase, 

243- 

Classification of grounds, 212. 
Cleats, knobs, moulding, 126. 



INDEX 



261 



Coal consumption, 162. 

Coal and lamp wear, 162. 

Combination fixture work, 150. 

Combination of two- and three- 
wire circuits, 107. 

Combination of two- and three- 
wire system, 109. 

Commercial and electrical effi- 
ciency, 1 1 8. 

Comparison of inductance and 
reactance, 236. 

Comparison of size of wire with 
two- and three-wire system, 
105. 

Comparative table of drop cir- 
cular mils and sizes, 71. 

Comparative table of regular and 
calculated sizes, 53. 

Complete cycle, 238. 

Complete panel switchboard, 203. 

Compound generators, speed of, 
182. 

Compound wound dynamos, 84. 

Compound wound generator con- 
nections, 171. 

Concealed work, 147. 

Conditions of switchboard de- 
sign, 189. 

Conduit concealed and exposed, 
127. 

Conduit in new buildings, 127. 

Conduit in old buildings, 127. 

Conduit, kinds of, 128. 

Conduits or tubes defined, 140. 

Conduit requirements, 141. 

Conduit system, laying out of a, 
144. 



Conduit wiring, 125. 
Connecting two-shunt wound 

generators, 173. 
Connections of shunt generator, 

169. 
Connections of street railway 

switchboard, 205. 
Connections of two-phase motor, 

251- 

Connections of three-phase mo- 
tor, 252. 

Control and light regulation, 167. 

Control of floors, 1 78. 

Converters, rotary, 218. 

Copper deposited by one cou- 
lomb, 19. . 

Copper required for alternating 
current wires, 249. 

Copper saved, 62. 

Cost and percentage of drop, 65. 

Cost of installation and material, 
64. 

Cost of light and life of lamp, 86. 

Cost of lost light, 161. 

Cosine of angle, value of, 240. 

Cosines, table of, 241. 

Couplings for joining conduit, 
136- 

Covering of wires and cables, 217. 

Cross section and resistance of 
wires, 25, 61. 

Current in branch circuits, 88. 

Current distribution in wires, 44. 

Current in each part of the cir- 
cuit, 43. 

Current in the wire, 43. 

Current, lag of, 228. 



262 



INDEX 



Current, a wattless, 239. 
Cycle, zero points of, 227. 

D 

Damp basements, 215. 

Day's light and coal, 162. 

Degradation of electrical energy, 
225. 

Degrees of a cycle, 238. 

Definition of angle of lag, 239. 

Definition of the ampere, 18. 

Definition of the mil, 25. 

Definition of a period, 122. 

Definition of tubes or conduits, 
140. 

Definition of wiring, 15. 

Detecting breaks in line, 215. 

Determination of two-phase cir- 
cuits, 258. 

Development of wiring table, 51. 

Diagram of four centers of distri- 
bution, 80. 

Diagram of limited drop, 78. 

Diagram of shunt generators in 
multiple, 173. 

Diagram of three-wire system, 
balanced, 107. 

Diagram of wattless current, 240. 

Differential voltmeters, 195. 

Differentially wound motor, 113. 

Distribution of current in wires, 

44- 

Distribution of lamps, 165. 
Distribution of power by ro- 

taries, 221, 222. 
Distribution of power, 255. 
Distribution, sub-centers of, 77. 



Distribution sheet, 152. 

Drilling the marble, 190. 

Drop affected by temperature, 
41. 

Drop calculated, 24, 26. 

Drop in the armature, 83. 

Drop in branch arms, 89. 

Drop in buildings, 85. 

Drop and circular mils, 31. 

Drop and size of feeders, mains, 
branches, 68. 

Drop of potential, 23. 

Drop per 1000 feet per ampere, 
60. 

Drop in Wiedemann system, 49. 

Dry goods and department stores, 
1 66. 

Dynamos for incandescent light- 
ing, 79- 

Dynamos, shunt and compound 
wound, 84. 



Effect of back EMF., on wiring, 

US- 
Effect of capacity on an alterna- 
ting current, 231. 

Effect of center of distribution on 
drop, 73. 

Effect of frequency, 228. 

Effects of high pressure on light, 
1 60. 

Effect of inductance on an alter- 
nating current, 230. 

Effect of overload, 180. 

Effect of resistance on electricity, 
225. 



INDEX 



263 



Effect of resistance on an alterna- 
ting current, 230. 

Effect of volts on weight of cop- 
per, 102. 

Efficiency of motors, 117. 

Efficiency of motors and circular 
mils, 1 20. 

Efficiency of motors and weight 
of wire, 121. 

Efficiency of rotary converters, 

221. 

Electric light system, items of, 37. 

Electric lighting, rotaries em- 
ployed for, 254. 

Electrolytic work, switchboards 
for, 197. 

Elements of an alternator, 122. 

Elements of a transmission plant, 

253- 

Elements of a wiring system, 63. 

EMF. formula for dynamos, 79. 

Enameled iron conduit, 129. 

Equal resistances in multiple, 33. 

Equalizer bar, 181. 

Equalizing generators, 183. 

Equalizing the pressure, 74. 

Equipment of streets with three- 
wire system, 103. 

Estimating circular mils and 
gauge number, 58. 

Estimating on conduit work, 153. 

Example of center of distribution, 
72. 

Examples of drop of potential, 36. 

Exposed and concealed conduit, 
127. 

Exposed work, 147. 



Factors, power, 246. 

False resistance, 229. 

Features of alternating currents, 

223. 

Feeders, branches, mains, 66. 
Feeder panel, back and front, 

202. 

Feeder panels, 196. 
Feeder switchboard, illustrated, 

200. 
Feeding system of street railway, 

204. 
Fire underwriters, approval of 

conduit work, 142. 
Flexible cord, steel armored, 136. 
Flexible metallic conduit, 128. 
Flexible non-metallic conduit, 

128. 

Flexible tubing, 131. 
Floors controlled, 178. 
Formula for calculating EMF. in 

dynamo, 79. 
Formula for calculating size of 

wire, 30. 
Formula for effect of heat on 

wires, 41. 
Formula for induction reactance, 

233- 

Formula for impedance, 235. 
Formula for three-phase wiring, 

247. 
Formula for three-wire system, 

106. 
Forward pressure of inductance, 

226. 



264 



INDEX 



Frequency, 123. 

Frequency, effect of, 228. 

Front and back of feeder panel, 

202. 

Fuses, 172. 
Fuse panels, 196. 



General principles of switch- 
board construction, 206. 

Generation of EMF., 114. 

Generator panels, 194. 

Generator switchboard, illus- 
trated, 199. 

Generators equalized, 183. 

Getting size of wire in electric 
lighting, 57. 

Globes and light, 164. 

Ground detector, 171. 

Ground detector, operation of, 
209. 

Ground detector, principle of, 
210. 

Ground detector for three-wire 
system, 211. 

Grounded circuits, location of, 
214. 

Grounded wires, 150. 

H 

Henry, unit of self induction, 236. 
High tension arc lighting, 28. 
Hooded insulators, 216. 
How ground is detected, 212. 
How the EMF. is varied, 81. 
Hygienic benefits of electric light- 
ing, 1 6. 



Illustration of sub-station distri- 
bution, 255. 

Impedance, calculation of, 235. 

Incandescent lamps, 85. 

Incandescent lamps, light of, 158. 

Incandescent lighting, dynamos 
for, 79. 

Individual mains, 67. 

Inductance and capacity, 232. 

Inductance in an alternating cur- 
rent circuit, 226. 

Inductance compared with re- 
sistance, 229. 

Inductance, with entering cur- 
rent, 237. 

Inductance and lag, 231. 

Inductance with leaving current, 

237- 

Inductance, principle of, 225. 

Induction motor, 249. 

Induction motor parts, 250. 

Induction reactance, 233. 

Installation of conduit, 145. 

Installation and material, cost of, 
64. 

Insulation of conductors, 145. 

Insulation of insulators, 216. 

Insulation, kinds of, 99. 

Insulation protected, 100. 

Insulation resistance, 94. 

Insulation resistance, limit of, 149. 

Insulation resistance measured, 
98. 

Insulation resistance of tall build- 
ings, 97. 



INDEX 



265 



Insulation resistance of wire, 95. 

Insulating joints, 150. 

Insulating materials for electrical 
work, 146. 

Intermediate sizes of wire calcu- 
lated, 56. 

Iron armored conduit, 128. 

Iron armored, accessories of, 138. 

Iron conduit requirements, 143. 

Items of an electric light system, 
37- 

J 

Joints, soldered, 151. 
Joining conduits by couplings, 

136. 
Junction boxes, 134. 



Kilowatt, meaning of, 39. 
Kinds of conduit, 128. 
Kinds of insulation, 99. 
Kinds of wiring, 125. 
Kirchoff's law, 88. 



Lag denned, 239. 

Lag of the current, 228. 

Lag and inductance, 231. 

Lamps, distribution of, 165. 

Lamp efficiency, 160. 

Lamp filaments, 86. 

Lamps in series, drop calculated, 

27. 

Large power stations, 220. 
Lamp rating, 159. 
Laying out a conduit system, 144. 



Length of wire and drop, 26. 

Life of a lamp, 17. 

Life of lamps and cost of light, 
86. 

Light and efficiency, 160. 

Light and globes, 164. 

Light effect with shades and 
globes, 164. 

Light obtained from low pres- 
sure, 163. 

Light of lamps, 158. 

Light per square foot, 163. 

Lightning arresters, 201. 

Lightning arresters, principle of, 
206. 

Lighting by the three-wire sys- 
tem, 101. 

Lighting circuits, apparatus of, 
176. 

Lighting circuit, power factors, 
248. 

Lighting system, two-phase, 255. 

Limited drop diagram, 78. 

Limit of insulation resistance, 

149- 
Line capacity, 224. 
Line losses, with alternating cur- 
rents, 223. 
Load panels, 195. 
Locating grounded circuits, 214. 
Lost light, cost of, 161. 
Lamp pressure, 17. 

M 

Magneto, testing with, 213. 
Mains, feeders, branches, 66. 
Marble for switchboards, 147. 



266 



INDEX 



Meaning of a coulomb, 19. 

Meaning of a kilowatt, 39. 

Meaning of L, 237. 

Meaning of self induction, 225. 

Meaning of the volt, 18. 

Measurement of insulation resis- 
tance, 98. 

Measurement of volts, 18. 

Measuring resistance of lamp, 
hot, 93. 

Mechanical work of conduit in- 
stallation, 145. 

Method of calculating circular 
mils for motors, 119. 

Method of getting all wire sizes, 

5, 5i>52, 53, 54, 55, 56, 57- 

Mil denned, 25. 

Motor connections, 113. 

Motor, induction, 249. 

Motor line, calculation of, 59. 

Motors, efficiency of, 117. 

Motors, single phase, 251. 

Motors, synchronous, 251. 

Motors, types of, 112. 

Mounting apparatus on slate, 
191. 

Mounting of lightning arresters, 
201. 

Movement of waves, 229. 

Multiple circuits, 33. 

Multiple connections of two- 
shunt machines, 173. 

Multiple wiring, 29. 

N 

Names of switchboard sections, 
193- 



National electrical code, 157. 
Neutral wire, 104. 

O 

Ohms, circular mils, and feet of 
wire, 33. 

Ohm's law, 17. 

One and two centers of distribu- 
tion, 75. 

Operation of the ground detector, 
209. 

Outlet and junction boxes, 134. 

Over compounding, 184. 

Over compounding, per cent, of, 
185. 

Overload effect, 180. 



Panel boards, 154. 

Panel board requirements, 156. 

Panel switchboards, 192. 

Panel switchboards analyzed, 

198. 
Parts of switchboards for D. C. 

generators, 208. 
Per cent, of over compounding, 

185. 

Percentage of drop, 29. 
Percentage of drop and cost, 65. 
Period defined, 122. 
Petticoat insulators, 216. 
Pilot lamp, 171. 
Plain unarmored, accessories of, 

138. 
Plan of lighting and switches, 

152. 
Points about motors, 116. 



INDEX 



267 



Potential, drop of, 23. 

Power calculated, 38. 

Power, distribution of, 255. 

Power factors, 246. 

Power factors for lighting circuit, 

248. 

Power factors, table of, 245. 
Practical connections of a shunt 

motor, 117. 

Pressure and illumination, 161. 
Principle of lightning arresters, 

207. 
Principle of the ground detector, 

210. 

Principle of the motor, 113. 
Principle of the three-wire sys- 
tem, 101. 
Principle of wiring a shunt motor, 

116. 

Protection of circuits, 169. 
Protection of insulation, 100. 
Purpose of analysis of wiring, 

46. 

Purpose of equalizer, 181. 
Purpose of flexible steel armored 

conduit, 135. 
Purpose of rotaries, 219. 
Purpose of series winding, 185. 
Purpose of two-phase currents, 

256. 
Purpose of wiring, 17. 



Rating of lamps, 159. 
Reactance, calculation of, 233. 
Rear view of switchboard, two- 
shunt machines, 177. 



Reasons for employing conduit, 

124. 

Recording wattmeter, 201. 
Regulation and control of lights, 

167. 

Regulation of EMF., 81. 
Reinforcement of trolley line, 

204. 
Relationship between coulombs 

and amperes, 20. 
Relationship between coulombs, 

copper, and amperes, 20. 
Relationship expressed by Ohm's 

law, 1 8. 
Relationship of watts, volts, and 

amperes, 38. 

Requirements for conduit, 141. 
Requirements for iron conduit, 

143- 

Requirements for steel-armored 
conduit, 143. 

Resistance and circular mils, 32. 

Resistance and cross section of 
wires, 61. 

Resistance and inductance com- 
pared, 236. 

Resistance effected by tempera- 
ture, 41. 

Resistance in multiple, 33. 

Resistance of equalizer bar, 183. 

Resistance of insulation, 94. 

Resistance of lamp measured 
cold, 93. 

Resistance of wires, 24. 

Rheostat, 171. 

Rheostat as a regulator, 83. 

Rheostatic regulation, 179. 



268 



INDEX 



Risk in connecting shunt gener- 
ators, 174 

Rotaries, application of, 220. 

Rotaries for power distribution, 
221. 

Rotaries in electric lighting, 254. 

Rotaries in power transmission, 
252. 

Rotary converters, 218. 

Rotor, 249. 

Rotor of motor, 250. 

Rubber-covered wires, 41. 

Rule for calculating equal re- 
sistances in multiple, 34. 

Rule for constructing wiring table, 
54- 



Safe operation of generators, 181. 
Saving in copper, 62. 
Schedule for wiring system, 140. 
Sections of switchboard, 193. 
Self-starting alternating current 

motors, 256. 
Separate mains, 67. 
Separation of EMF. and C., 228. 
Series, coil of generator, 181. 
Series, electric lighting, 28. 
Series, fields, 184. 
Series, field shunt resistance, 186. 
Series, wound motor, 113. 
Shunt dynamos, 83. 
Shunt generator, connections of, 

169. 
Shunt resistance of series field, 

1 86. 
Shunt wound motor, 1 13. 



Single and double pole circuit 

breakers, 192. 

Single phase calculations, 243. 
Single phase motors, 251. 
Sizes of wire and circular mils, 31. 
Sizes of wire calculated by rule, 

55- 

Size of wire for alternating cur- 
rent mains, 242. 

Size of wire for motors calcu- 
lated, 1 1 8. 

Size of wire with two- and three- 
wire systems, 105. 

Slate drilled for apparatus, 190. 

Soldering fluid, 151. 

Special insulation, 147. 

Speed of compound generators, 
182. 

Squirrel cage rotors, 251. 

Station fires through lightning, 
208. 

Stator of motor, 250. 

Steel armored conduit require- 
ments, 143. 

Steel armored flexible cord, 136. 

Step down transformers, 253. 

Step up transformers, 253. 

Strain on insulators, 215. 

Street railway, generator and 
feeder, switchboard sections, 
205. 

Street railway plants, 186. 

Street railway switchboard, 204. 

Sub-centers of distribution, 77. 

Sub-divisions of a railway board, 
204. 

Sub-station distribution, 255. 



INDEX 



269 



Sub-stations, rotaries for, 255. 

Sub-stations, use of, 219. 

Switchboards, 168. 

Switchboard apparatus, 168. 

Switchboard design, 188. 

Switchboards for electrolytic 
work, 197. 

Switchboard for lighting, 176. 

Switchboard for street railway 
work, 204. 

Switchboard marble, 147. 

Switchboard, rear view of connec- 
tions of two shunt machines, 
177. 

Switchboard requirements, 156. 

Switchboard with control of 
floors, 178. 

Synchronous motors, 251. 

System of wiring for two floors, 
69. 



Table of amperes in wiring and 

insulation resistance, 149. 
Table of asphaltic paper conduit, 

!3i- 
Table of brass armored conduit, 

ISO- 
Table of copper and insulation 

resistance, 96. 
Table of cosines, 241. 
Table of coulombs and amperes, 

20. 

Table of different centers of dis- 
tribution, 74. 



Table of distance, watts, drop, 
and size, 62. 

Table of drop and circular mils 
for branches, 70. 

Table of drop and circular mils 
for feeders, 70. 

Table of drop and circular mils 
for mains, 70. 

Table of drop in a line, 24. 

Table of drop per 1,000 feet per 
ampere, 60. 

Table of efficiency and circular 
mils for motors, 120. 

Table of enameled iron conduit, 
130. 

Table of feet of wire and insula- 
tion resistance, 96. 

Table of flexible metallic conduit, 
132. 

Table of flexible steel armored 
conduit, 137. 

Table of flexible woven conduit, 
132. 

Table of floors, outlets and pur- 
pose, 153. 

Table of gauge number and 
drop per 1,000 feet per ampere, 
61. 

Table of horse power and effi- 
ciency, 119. 

Table of iron armored conduit, 
129. 

Table of intermediate sizes of 
wire, 56. 

Table of lamp drop in Wiede- 
mann system, 49. 

Table of power factors, 245. 



270 



INDEX 



Table of relationship of watts, 

. volts, and amperes, 38. 

Table of resistance, cross section, 

and length of wire, 26. 
Table of resistance and cross 

section of wires, 25. 
Table of sections of switchboards, 

208. 

Table of sizes of wire, 55. 
Table of temperature coefficients, 

42. 
Table of turns, speed, lines of 

force and volts, 81. 
Table of unequal resistance in 

multiple, 36. 
Table of volts and light efficiency, 

163. 
Table of watts per candle power, 

159- 

Table of wiring, 50, 51, 52. 

Table showing effect of field 
changes on volts, 82. 

Table with amperes constant, 
21. 

Table with ohms constant, 22. 

Table with volts constant, 21. 

Temperature affecting resistance 
and drop, 41. 

Temperature coefficients, 42. 

Testing circuits, 87, 209. 

Testing with a magneto, 213. 

Testing with a voltmeter, 212. 

Telegraph lines, insulation resis- 
tance of, 97. 

The alternating current, 121. 

The power factor, 238. 



The resistance box, 83. 

The three- wire system, 101. 

The wiring table, 50, 51, 52. 

The Wheatstone bridge, 87. 

Theory of the Wheatstone bridge, 
90. 

Three centers of distribution, 
76. 

Three-phase alternator connec- 
tions, 257. 

Three-phase, calculation of wire 
for, 247. 

Three-phase circuit, 245. 

Three-phase motor connections, 
252. . 

Three-phase system, 256. 

Three-wire panel boards, 155. 

Three-wire system for lighting, 
101. 

Tools for conduit work, 138. 

Transformers, auto, 249. 

Transformers, step down, 253. 

Transformers, step up, 253. 

Transformer, winding, 254. 

Transmission plant, elements of, 

253. 

Two-phase alternator connec- 
tions, 257. 

Two-phase circuits determined, 
258. 

Two-phase lighting system, 255. 

Two-phase mains, calculation of, 
244. 

Two-phase motor connections, 
251. 

Two-floor system of wiring, 69. 



INDEX 



271 



Two- wire panel boards, 154. 
Two- wire system ground detector, 

2IO. 

Two-wire 22O-volt system, 103. 
Type of glass and effective light, 

164. 
Types of motors, 112. 



U 

Unarmored conduit, 128. 

Unbalanced three-wire system, 
104. 

Underwriters' laws for panel 
boards, 155. 

Underwriters' laws for switch- 
boards, 155. 

Unequal resistances in multiple, 

34- 

Unit of self-induction, 236. 
Use of bridge, 91. 
Use of bus bars, 175. 
Use of chandeliers, 166. 
Using solder for joints, 151. 



Value of capacity reactance, 

234- 

Value of cos. of angle, 240. 
Value of induction reactance, 

233- 

Various power equipments, 219. 
Ventilation of New York Stock 

Exchange, 17. 



Voltmeter, differential, 195. 
Volts lost and length of wire, 
26. 

W 

Waste of light through globes, 

164. 

Wattless current, 239. 
Watts per candle power, at low 

pressure, 163. 

Waves of alternating EMF., 227. 
Weatherproof wire, 217. 
Weight of copper and efficiency 

of motor, 121. 
Weight of -copper for mains, 

249. 
Weight of copper and pressure, 

IO2. 

Weight of wire calculated, no. 
Wheatstone bridge, theory of, 

90. 
Wheatstone bridge, resistances, 

89. 
Wiedemann system, 46, 47, 48, 

49, 5- 

Wiedemann wiring analyzed, 47, 
48. 

Wires, calculation of resistance 
of, 25. 

Wires, carrying capacity of, 40. 

Wires, cross section and resist- 
ance, 25. 

Wires, rubber covered, 41. 

Wire sizes for open and con- 
cealed work, 148. 



272 



INDEX 



Wires underground, 125. 

Wiring denned, 15. 

Wiring formula, 30. 

Wiring by the Wiedemann sys- 
tem, 46, 47. 

Wiring for three-wire system, 
108. 

Wiring for single phase, 243. 

Wiring systems for conduit, 139. 



Wiring system, elements of, 63. 
Wiring table developed, 52. 
Wiring table rule, 54. 
Wiring with steel armored flex- 
ible conduit, 135. 
Winding of transformer, 254. 



Zero points in one cycle, 227. 



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W r RIGHT. Electric Furnaces and Their Industrial Applications. 

Contains 285 pages, and 57 illustrations, which are essentially 
in the nature of sectional diagrams, representing principles of 
construction. This is a timely and practical treatise on the forms 
and uses of electric furnaces in modern electro-chemical pro- 
cesses. Price, $3.00. 



JUST PUBLISHED. 

Electrician's Handy Book. 

BY 
T. O'COIMOR SLOANE, A. M., E, M., PH. D 

Handsomely Bound in Red Leather, with Titles and 
Edges in Gold, 

POCKET BOOK STYLE. 
PRICE $3.50 

A THOROUGHLY practical up-to-date book of 768 pages, covering 
the entire field of electricity. Contains no useless theory. Every- 
thing in it is to the point, and can be easily understood by the student, the 
practical worker, and the every-day working electrician. The advanced 
electrical engineer will also receive great benefit from its perusal and study. 

It is a work of the most modern practice, written in a clear, compre- 
hensive manner, and covers the subject thoroughly, beginning at the ABC 
of the subject, and gradually takes you to the more advanced branches of 
the science. It teaches you just what you should know about electricity. 

A practical work for the practical man. Contains 41 chapters and 
whenever the te.it can be simplified by means of an illustration, an illustra- 
tion is given. There are consequently throughout the work no less than 
610 specially made engravings. It is the standard work on the subject. 
There is not a student, engineer, electrician, business manager or foreman 
who can afford to be without the information contained in its pages. You 
are doing yourself an injustice if you don't procure this book at once. 



THE NORMAN W, HENLEY PUBLISHING CO,, 

PUBLISHERS, 
132 NASSAU STREET, NEW YORK, U. S. A, 



JUST ISSUED. 

ELECTRIC WIRING, DIAGRAMS 

AND SWITCHBOARDS. 

BY NEWTON HARRISON, E. E., 

INSTRUCTOR IN ELECTRICAL ENGINEERING IN THE 
NEWARK TECHNICAL SCHOOL. 

250 Pages Very Fully Illustrated 

PRICE $1.50 

A THOROUGHLY practical treatise on the subject of Electric Wiring 
in all its branches, including explanations and diagrams which are 
thoroughly explicit and greatly simplify the subject. Practical 
every-day problems in wiring are presented and the method of obtaining 
intelligent results clearly shown. Only arithmetic is used. Ohm's law is 
given a simple explanation with reference to wiring for direct and alter- 
nating currents. The fundamental principle of drop of potential in cir- 
cuits is shown with its various applications. The simple circuit is 
developed with the position of mains, feeders and branches ; their treat- 
ment as a part of a wiring plan, and their employment in house wiring 
clearly illustrated. 

CONTAINING SPECIAL CHAPTERS ON: 

The Beginning of Wiring; Calculating the Size of Wire; a Simple Electric 
Ivight Circuit Calculated ; Estimating of Mains, Feeders and Branches; Using the 
Bridge for Testing; the Insulation Resistance; Wiring for Motors; Wiring with 
Cleats, Moulding and Conduit; paying out a Conduit System; Power Required for 
I^amps ; lighting of a Room ; Switchboards and their Purpose ; Switchboards 
Designed for Shunt and Compound Wound Dynamos; Panel Switchboards; 
Street Railway Switchboards; lightning Arresters; the Ground Detector; Locat- 
ing Grounds ; Alternating Current Circuits; the Power Factor in Circuits; Calcu- 
lation of Sizes of Wire for Single, Two and Three-Phase Circuits. 



THE NORMAN W. HENLEY PUBLISHING CO., 

PUBLISHERS, 

132 NASSAU STREET. NEW YORK, U. S. A. 



THIS BOOK IS DUE ON THE LAST DATE 
STAMPED BELOW 



AN INITIAL FINE OF 25 CENTS 

WILL BE ASSESSED FOR FAILURE TO RETURN 
THIS BOOK ON THE DATE DUE. THE PENALTY 
WILL INCREASE TO 5O CENTS ON THE FOURTH 
DAY AND TO $I.OO ON THE SEVENTH DAY 
OVERDUE. 



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UNIVERSITY OF CALIFORNIA LIBRARY